Planar inviscid flows in a channel of finite length : washout, trapping and self-oscillations of vorticity

The paper addresses the nonlinear dynamics of planar inviscid incompressible flows in the straight channel of a finite length. Our attention is focused on the effects of boundary conditions on vorticity dynamics. The renowned Yudovich's boundary conditions (YBC) are the normal component of velocity given at all boundaries, while vorticity is prescribed at an inlet only. The YBC are fully justified mathematically: the well posedness of the problem is proven. In this paper we study general nonlinear properties of channel flows with YBC. There are 10 main results in this paper: (i) the trapping phenomenon of a point vortex has been discovered, explained and generalized to continuously distributed vorticity such as vortex patches and harmonic perturbations; (ii) the conditions sufficient for decreasing Arnold's and enstrophy functionals have been found, these conditions lead us to the washout property of channel flows; (iii) we have shown that only YBC provide the decrease of Arnold's functional; (iv) three criteria of nonlinear stability of steady channel flows have been formulated and proven; (v) the counterbalance between the washout and trapping has been recognized as the main factor in the dynamics of vorticity; (vi) a physical analogy between the properties of inviscid channel flows with YBC, viscous flows and dissipative dynamical systems has been proposed; (vii) this analogy allows us to formulate two major conjectures (C1 and C2) which are related to the relaxation of arbitrary initial data to C1: steady flows, and C2: steady, self-oscillating or chaotic flows; (viii) a sufficient condition for the complete washout of fluid particles has been established; (ix) the nonlinear asymptotic stability of selected steady flows is proven and the related thresholds have been evaluated; (x) computational solutions that clarify C1 and C2 and discover three qualitatively different scenarios of flow relaxation have been obtained

Inviscid instability of an incompressible flow between rotating porous cylinders to three-dimensional perturbations

We consider the stability of the Couette-Taylor flow between porous cylinders with radial throughflow in the limit of high radial Reynolds number. It has already been shown earlier that this flow can be unstable to two-dimensional perturbations. In the present paper, we study its stability to general three-dimensional perturbations. In the limit of high radial Reynolds number, we show the following: (i) the purely radial flow is stable (for both possible directions of the flow); (ii) all rotating flows are stable with respect to axisymmetric perturbations; (iii) the instability occurs for both directions of the radial flow provided that the ratio of the azimuthal component of the velocity to the radial one at the cylinder, through which the fluid is pumped in, is sufficiently large; (iv) the most unstable modes are always two-dimensional, i.e. two-dimensional modes become unstable at the smallest ratio of the azimuthal velocity to the radial one; (v) the stability is almost independent of the rotation of the cylinder, through which the fluid is being pumped out. We extend these results to high but finite radial Reynolds numbers by means of an asymptotic expansion of the corresponding eigenvalue problem. Calculations of the first-order corrections show that small viscosity always enhances the flow stability. It is also shown that the asymptotic results give good approximations to the viscous eigenvalues even for moderate values of radial Reynolds number

Three Science Fiction/Comedy Short Stories

This project was about creative writing and describes the process that I used to develop my stories. It contains three short stories that I wrote for an imaginary magazine called Creative Galaxy

Chromosomal-level assembly of the Asian Seabass genome using long sequence reads and multi-layered scaffolding

We report here the ~670 Mb genome assembly of the Asian seabass (Lates calcarifer), a tropical marine teleost. We used long-read sequencing augmented by transcriptomics, optical and genetic mapping along with shared synteny from closely related fish species to derive a chromosome-level assembly with a contig N50 size over 1 Mb and scaffold N50 size over 25 Mb that span ~90% of the genome. The population structure of L. calcarifer species complex was analyzed by re-sequencing 61 individuals representing various regions across the species' native range. SNP analyses identified high levels of genetic diversity and confirmed earlier indications of a population stratification comprising three clades with signs of admixture apparent in the South-East Asian population. The quality of the Asian seabass genome assembly far exceeds that of any other fish species, and will serve as a new standard for fish genomics

Single haplotype assembly of the human genome from a hydatidiform mole

A complete reference assembly is essential for accurately interpreting individual genomes and associating variation with phenotypes. While the current human reference genome sequence is of very high quality, gaps and misassemblies remain due to biological and technical complexities. Large repetitive sequences and complex allelic diversity are the two main drivers of assembly error. Although increasing the length of sequence reads and library fragments can improve assembly, even the longest available reads do not resolve all regions. In order to overcome the issue of allelic diversity, we used genomic DNA from an essentially haploid hydatidiform mole, CHM1. We utilized several resources from this DNA including a set of end-sequenced and indexed BAC clones and 100× Illumina whole-genome shotgun (WGS) sequence coverage. We used the WGS sequence and the GRCh37 reference assembly to create an assembly of the CHM1 genome. We subsequently incorporated 382 finished BAC clone sequences to generate a draft assembly, CHM1_1.1 (NCBI AssemblyDB GCA_000306695.2). Analysis of gene, repetitive element, and segmental duplication content show this assembly to be of excellent quality and contiguity. However, comparison to assembly-independent resources, such as BAC clone end sequences and PacBio long reads, indicate misassembled regions. Most of these regions are enriched for structural variation and segmental duplication, and can be resolved in the future. This publicly available assembly will be integrated into the Genome Reference Consortium curation framework for further improvement, with the ultimate goal being a completely finished gap-free assembly

Avenants aux commandes : comment administrer les avenants d’une façon efficiente ?

During my alternative time within the Procurement department of Alstom Power Steam, I was given the task to manage a sourcing portfolio including a number of different specifications. Main orders having been mostly already negotiated and confirmed, my main task became dealing with amendments to order. Already in my discovery report did I wonder about the high numbers of amendments, their origin, background and reasons? When suggesting this could be an interesting theme for my end of study Memoir, my manager indicated that to his knowledge no study had been achieved on the matter before. The first aim for this report would then be to obtain a thorough description of the existing situation: 1) How many amendments for each project and spec? 2) What extra spend did those represent, and what was the administrative costs attached to proceeding them? 3) Where were they originated, and with what reason? 4) How were they looked upon and considered within the Procurement department, engineering or Quality? Thanks to the analysis made and internal interviews I was able to elaborate an answer to this first question: amendments should globally be considered as negative for the organization except for a few specific cases. However the positive side never covers the risks related to a greater number of amendments, and it becomes essential to improve their daily management. This first answer brings us to our next point: How to improve the management of amendments in a most efficient manner? After having introduced ALSTOM and its different parts, the background of my mission, I will develop within this document what has been my logic and rationale to better cope with some of the questions concerning Procurement Management.Dans le cadre de mon alternance au sein du service « Procurement » d’Alstom Power Steam, je me suis vu confier la gestion d’un portefeuille achats comportant plusieurs spécifications différentes. Les commandes principales étant pour la plupart déjà négociées et signées, je me suis principalement occupé des avenants aux contrats. C’est dans un rapport d’étonnement que je me suis alors posé la question du nombre important d’avenants, de leurs origines et de leurs causes. En proposant ce sujet de mémoire, mon responsable m’a alors indiqué qu’à sa connaissance aucune étude n’avait été menée sur cette problématique. Le premier objectif de ce mémoire serait donc de réaliser un état des lieux de l’existant : 1) Combien d’avenants créés par projets et par spécifications ? 2) Dépenses liées aux avenants, leurs coûts administratifs ; 3) Quelles provenances exactes, quelles causes ? 4) Quel regard est porté sur les avenants, comment sont-ils considérés par le service achats, les ingénieurs, les qualiticiens, etc. J’ai ensuite souhaité comparer les données sur trois projets différents afin de voir si certaines spécifications pouvaient être plus génératrices d’avenants que d’autres et quelles en seraient les raisons éventuelles. Enfin et pour poser et répondre à ma première problématique, j’ai cherché (grâce à des entretiens réalisés en interne) à définir si les avenants étaient à considérer comme néfastes ou bénéfiques pour l’entreprise. Grâce à l’analyse des études menées sur les projets et les entretiens internes, j’ai pu apporter une réponse à cette première problématique : les avenants sont globalement néfastes pour l’organisation mais peuvent être bénéfiques dans certains cas spécifiques. Cependant, le côté positif ne couvre pas le risque lié à l’utilisation d’un trop grand nombre d’avenants et il est important de mieux les gérer dans l’organisation. Cette réponse m’a permis d’ouvrir ma recherche sur une seconde problématique : comment administrer les avenants d’une façon plus efficiente ? Après avoir présenté dans un premier temps l’entreprise Alstom, ses différentes composantes et le contexte de la mission, je vais tenter dans ce mémoire d’expliquer quelle a été ma démarche et ma logique pour répondre au mieux à certaines problématiques du service achat