Contribution to the study of efficient iterative methods for the numerical solution of partial differential equations

Multigrid and domain decomposition methods provide efficient algorithms for the numerical solution of partial differential equations arising in the modelling of many applications in Computational Science and Engineering. This manuscript covers certain aspects of modern iterative solution methods for the solution of large-scale problems issued from the discretization of partial differential equations. More specifically, we focus on geometric multigrid methods, non-overlapping substructuring methods and flexible Krylov subspace methods with a particular emphasis on their combination. Firstly, the combination of multigrid and Krylov subspace methods is investigated on a linear partial differential equation modelling wave propagation in heterogeneous media. Secondly, we focus on non-overlapping domain decomposition methods for a specific finite element discretization known as the hp finite element, where unrefinement/refinement is allowed both by decreasing/increasing the step size h or by decreasing/increasing the polynomial degree p of the approximation on each element. Results on condition number bounds for the domain decomposition preconditioned operators are given and illustrated by numerical results on academic problems in two and three dimensions. Thirdly, we review recent advances related to a class of Krylov subspace methods allowing variable preconditioning. We examine in detail flexible Krylov subspace methods including augmentation and/or spectral deflation, where deflation aims at capturing approximate invariant subspace information. We also present flexible Krylov subspace methods for the solution of linear systems with multiple right-hand sides given simultaneously. The efficiency of the numerical methods is demonstrated on challenging applications in seismics requiring the solution of huge linear systems of equations with multiple right-hand sides on parallel distributed memory computers. Finally, we expose current and future prospectives towards the design of efficient algorithms on extreme scale machines for the solution of problems coming from the discretization of partial differential equations

An investigation into the use of gaussian processes for the analysis of microarray data

Master'sMASTER OF ENGINEERIN

Programmed Translational Readthrough in Drosophila melanogaster

Translational readthrough (TR) is extensively used by viruses to expand their limited genome capacity. The pervasiveness of TR across eukaryotic genomes is only recently being explored. Systems biology approaches such as comparative phylogenetics, combined with ribosome profiling studies have led to the identification of several hundred genes that can undergo TR in Drosophila melanogaster. However, only limited number of these genes have been experimentally studied. Due to the lack of systemic biochemical studies, the actual mechanism of TR regulation and the role of regulated TR in proteome expansion in D. melanogaster remains largely unexplored. In this study, we develop a dual luciferase reporter assay system to analyze a set of genes from D. melanogaster that have been phylogenetically predicted to undergo TR. We provide experimental validation and quantification of the extent of TR in these genes and also analyze the impact of immediate stop codon context on TR modulation. For one particular candidate, aPKC, we use systematic mutational analysis to delineate the minimal primary sequence motif responsible for driving efficient TR. Furthermore, in order to understand the biological significance and phenotypic outcome of gene-specific TR, we employ CRISPR/Cas9-based genome editing to create genetic mutants of the large Maf transcription factor, traffic jam (tj), that exhibit constitutive TR or abolished it. We identify tissue-specific regulation of TR in tj, wherein the expression of Tj-TR isoform is restricted to the nervous tissues. The TR extension selectively attenuates the native Tj function, specifically in the determination of morphogenetic behavior and spatial distribution of cap cells in adult ovaries. Conversely, the TR extension positively amplifies the selective gene regulatory function of native Tj in downregulation of the adhesion protein Fasciclin III. Using high-throughput RNA sequencing, we further dissect the role of TR in tj in shaping the transcriptome profile in adult brains. Our results hint towards a complex mode of regulation of Tj function by TR that operates via conditional fine-tuning of its specific gene regulatory functions

Proceedings of the International Micro Air Vehicles Conference and Flight Competition 2017 (IMAV 2017)

The IMAV 2017 conference has been held at ISAE-SUPAERO, Toulouse, France from Sept. 18 to Sept. 21, 2017. More than 250 participants coming from 30 different countries worldwide have presented their latest research activities in the field of drones. 38 papers have been presented during the conference including various topics such as Aerodynamics, Aeroacoustics, Propulsion, Autopilots, Sensors, Communication systems, Mission planning techniques, Artificial Intelligence, Human-machine cooperation as applied to drones

High-energy processes in low-mass protostars – an X-ray to radio multi-wavelength perspective

High-energy processes in protostars remain poorly understood. Only after the recently finished Chandra Orion Ultra-deep Project (COUP), statistically significant information on X-ray emission from Young Stellar Objects (YSOs) has been obtained. For an understanding of the mechanisms responsible for the X-ray emission, multi-wavelength correlations of flares, especially in the radio regime, are necessary and have become an active field of research. Magnetic fields cause several high-energy phenomena in the coronae of YSOs mainly due to magnetic reconnection which are observable in a wide wavelength range from nonthermal centimetric radio emission to X-rays. In this work, these processes were probed using a variety of very different methods which can be grouped into three major topics: X-ray to radio multi-wavelength variability of Young Stellar Objects The Coronet cluster in the nearby R~CrA dark cloud offers the rare opportunity to study a compact cluster of several very young protostars which are detected at radio- and X-ray wavelengths. Initially, a study focusing separately on X-ray and radio variability of these sources was conducted. Subsequently, in August 2005, the same region was studied in the first simultaneous X-ray, radio, near-infrared, and optical monitoring campaign of YSOs. Several observatories were observing simultaneously, namely the Chandra X-ray Observatory, the VLA, as well as telescopes with optical and near-infrared detectors in Chile and South Africa. Remarkable intra-band variability but no clearly correlated variability was found. This most importantly suggests that there is no direct link between the X-ray and optical/infrared emission and supports the notion that accretion is not an important source for the X-ray emission of these YSOs. Combining the Chandra X-ray data collected in the course of the multi-wavelength campaign with previous archival data, one of the deepest X-ray datasets ever obtained of a star-forming region is obtained and discussed.Radio emission from protostars Looking for compact nonthermal centimetric radio emission, high-sensitivity Very-Long-Baseline Interferometry (VLBI) observations of four nearby protostars were carried out, yielding the currently most sensitive data of such sources. Weak compact emission was found in the VLBI data of the class~0/I binary YLW15 VLA2, constraining the size of its corona to sub-AU scales. Since this source is part of a binary system with observed orbital motion, further VLBI observations will allow to quickly determine the orbit very accurately. The observed sources apparently were showing quiescent radio emission on the larger scales probed by the Very Large Array (VLA). Until now, only very few radio flares of YSOs have been observed in detail. In further work, two such examples are presented and analyzed: a flaring, deeply embedded protostar in Orion and a flaring binary T~Tauri system whose activity is due to inter-binary coronal interaction.The earliest stages: Magnetic fields in molecular clouds While mapping molecular clouds in polarized dust continuum emission has become a standard technique, the potentially more powerful technique using the "Goldreich-Kylafis" effect has been only rarely used until now. This effect predicts weakly linearly polarized molecular line emission under certain circumstances. By choosing different transitions, it is possible to probe the magnetic field direction in different regions in a molecular cloud core, and additionally one gets information along the line of sight for optically thin emission lines. The XPOL correlation polarimeter at the IRAM 30m telescope was used in a search for such linearly polarized emission in several bright molecular transition lines towards prominent star-forming regions. The combined effects of instrumental polarization and extended emission were simulated for a thorough interpretation of the results. In one case, the observed polarization exceeds the simulated instrumental value

Modélisation électromagnétique 3D d'inducteurs multibrins - Développement d'une méthode intégrale parallélisée

In order to enable to use high frequencies in the domain of the industrialinductive heating, the use of multi-wires inductors is considered. But, lossesoccurring into that inductors can be important and strongly depend on their complexinternal geometry. To facilitate the design of lossless multi-wires inductors, it isnecessary to under stand their electromagnetic behavior. In this thesis, we presentthe development of a software of parallel computation intended to the 3D electromagneticmodeling of multi-wires inductors. We describe an original method ofbuilding of the geometry of that inductors. This software is based on an integralmethod in which the meshing of spaces between the wires is unnecessary. The useof parallel computing is one of the great forces of this software. The studies werealized show the impact of the geometry on the behavior of that type of inductor.Afin de permettre l’utilisation de hautes fréquences dans le domainedu chauffage par induction industriel, l’emploi d’inducteurs multibrins est envisagé.Or, les pertes occasionnées dans ces inducteurs peuvent être importantes etdépendent fortement de leur géométrie interne qui est complexe. Pour faciliter laconception d’inducteurs multibrins à faibles pertes, il est nécessaire d’en comprendrele comportement électromagnétique. Dans cette thèse, nous présentons ledéveloppement d’un logiciel de calcul parallèle dévolu à la modélisation électromagnétique3D d’inducteurs multibrins. Nous décrivons une méthode originale deconstruction de la géométrie des inducteurs. Ce logiciel est basé sur une méthodenumérique de type intégrale ayant l’avantage de ne pas nécessiter le maillage desespaces entre les brins. L’emploi du calcul parallèle est une des grandes forces de celogiciel. Les études réalisées montrent l’impact de la géométrie sur le comportementde ce type d’inducteur

Pattern Recognition

Pattern recognition is a very wide research field. It involves factors as diverse as sensors, feature extraction, pattern classification, decision fusion, applications and others. The signals processed are commonly one, two or three dimensional, the processing is done in real- time or takes hours and days, some systems look for one narrow object class, others search huge databases for entries with at least a small amount of similarity. No single person can claim expertise across the whole field, which develops rapidly, updates its paradigms and comprehends several philosophical approaches. This book reflects this diversity by presenting a selection of recent developments within the area of pattern recognition and related fields. It covers theoretical advances in classification and feature extraction as well as application-oriented works. Authors of these 25 works present and advocate recent achievements of their research related to the field of pattern recognition