Spectral theorems for random walks on mapping class groups and Out(FN)\text{Out}(F_N)

We establish spectral theorems for random walks on mapping class groups of connected, closed, oriented, hyperbolic surfaces, and on $\text{Out}(F_N)$. In both cases, we relate the asymptotics of the stretching factor of the diffeomorphism/automorphism obtained at time $n$ of the random walk to the Lyapunov exponent of the walk, which gives the typical growth rate of the length of a curve -- or of a conjugacy class in $F_N$ -- under a random product of diffeomorphisms/automorphisms. In the mapping class group case, we first observe that the drift of the random walk in the curve complex is also equal to the linear growth rate of the translation lengths in this complex. By using a contraction property of typical Teichm\"uller geodesics, we then lift the above fact to the realization of the random walk on the Teichm\"uller space. For the case of $\text{Out}(F_N)$, we follow the same procedure with the free factor complex in place of the curve complex, and the outer space in place of the Teichm\"uller space. A general criterion is given for making the lifting argument possible.Comment: 45 pages, 3 figures. arXiv admin note: text overlap with arXiv:1506.0724

Canine reference intervals for coagulation markers using the STA Satellite and the STA-R Evolution analyzers

The aim of the current study was to determine canine reference intervals for prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen, and antithrombin (AT) according to international recommendations. The STA Satellite coefficients of variation of within-laboratory imprecision were 3.9%, 1.3%, 6.9%, and 5.1% for PT, APTT, fibrinogen, and AT, respectively. At 4uC, citrated specimens were stable up to 8 hr for whole blood and 36 hr for plasma, except for APTT, which increased slightly (<1 sec). Nonparametric reference intervals determined in citrated plasma from 139 healthy fasting purebred dogs were 6.9–8.8 sec, 13.1–17.2 sec, 1.24–4.30 g/l, and 104–188% for PT, APTT, fibrinogen, and AT, respectively. Based on Passing–Bablok comparison between STA Satellite and STA-R Evolution using 60 frozen specimens from a canine plasma bank, the corresponding reference intervals were transferred to the STA-R Evolution: 7.1–9.2 sec, 12.9–17.3 sec, 1.20–4.43 g/l, and 94–159% for PT, APTT, fibrinogen, and AT, respectively

Analyse Numérique de l'effet du RPM sur le décochage dynamique observé sur un rotor d'hélicoptère lors d'un vol d'avancement à forte charge

International audienceDynamic stall is a highly complex phenomenon characterized by unsteady massive separated flow. It limits the flight envelope of helicopters by generating vibrations and large dynamic loads which can lead to fatigue and structural failure of blades. Dynamic stall involves several mechanisms which make the numerical prediction of stall difficult and the understanding of the phenomenon still incomplete. A loose coupling methodology between a Computational Fluid Dynamics and a Comprehensive Analysis codes is used to simulate the problem. Three stalled flight conditions have been selected in the wind tunnel 7A rotor test data to investigate the RPM effect on the dynamic stall onset and the related mechanisms. The lower the RPM, the more severe the stall is. A double stall has been observed on the lowest RPM case. The coupled simulations are in satisfactory agreement with experiment and are used to identify the mechanisms leading to stall. Simulations indicate that the blade-vortex interaction is an important factor in triggering the different stall events in these configurations.Le décrochage dynamique est un phénomène complexe caractérisé par d'importants décollements de la couche limite. Il constitue une limite du domaine de vol des hélicoptères puisqu'il génère des vibrations ainsi que de fortes variations de charge sur les pales ce qui peut mener à la fatigue puis à la rupture de celles-ci. La prédiction du décrochage dynamique à l'aide d'outils de simulation est toujours difficile puisque de nombreux phénomènes complexes sont impliqués ainsi la compréhension du décrochage dynamique reste encore incomplète. Dans cette étude, des simulations de couplage faible entre le code de CFD elsA et le code de structure HOST sont réalisées sur trois configurations de vol issues d'essais en souffleries à Modane. L'objectif étant d'évaluer l'influence du RPM sur l'apparition du décrochage. Il est montré que plus le RPM est faible, plus le décrochage est intense. En effet, deux événements de décrochage successifs sont observés dans le cas avec le plus faible RPM. Les simulations sont en très bon accord avec les résultats expérimentaux et peuvent donc être exploités pour une analyse des mécanismes du décrochage. Il est montré également que l’interaction pale – tourbillons semble être un facteur important dans le déclenchement du décrochage

: groupe d'étude PREMODA

International audienceOBJECTIVES: In agreement with national guidelines published in 2007, limiting duration of expulsive efforts to 30 minutes is a common obstetrical practice in France. In many other countries, there is no fixed limit for pushing duration. The objective of our work is to analyze mode of delivery and neonatal issues according to duration of expulsive efforts. PATIENTS AND METHODS: It is a secondary analysis of an observational prospective study, among low-risk primiparous women, in 138 French maternity units. According to duration of expulsive efforts, we determined proportions of spontaneous and instrumental vaginal deliveries. Then, we analyzed the risk of neonatal asphyxia (defined by p

Histoires de fantômes : insoutenables légèretés et ombres portées de l’enfant dans le roman britannique contemporain

Chercher l’enfant dans le roman britannique contemporain, c’est souvent s’exposer au paradoxe de son omniprésence dans les discours, conjuguée à une forme d’absence physique. Dans The Child in Time, de McEwan, il disparaît avant même la diégèse pour apparaître chez Lessing ou Martin Amis sous la forme creuse du changeling. Dans When We Were Orphans, Ishiguro dessine un enfant voilé par les complaisances fallacieuses du souvenir, tandis que chez Byatt (The Children’s Book) les protagonistes se voient imposer par leur mère-écrivain un double fictionnel qui les déréalise. C’est cette singulière présence-absence, cette très légère façon qu’a l’enfant de se poser en littérature, qui semble avoir fasciné les romanciers contemporains, en ce que, objet littéraire non verbal (infans), et toujours l’autre de l’adulte qui l’écrit, il est d’abord un défi à la transparence mimétique, contraignant ceux qui l’écrivent à exhiber leurs filtres, souvent à travers une thématique assumée du faux, du leurre. La seconde transparence de l’enfant n’est pas strictement poïétique mais tient à sa représentation : défini par le déjà-là littéraire comme un idéal par l’absence (innocent, infans…), il attire l’investissement aliénant de toutes les valeurs jusqu’à devenir un signe blanc, une opacité herméneutique que certains romanciers cherchent aujourd’hui à conjurer en salissant l’enfant, mon(s)trant son corps pour mieux lui rendre l’ombre portée qui lui manquait. Une autre manière de travailler cet héritage spectral étant de laisser voir, en transparence, l’épaisseur feuilletée de palimpseste de l’enfant : plutôt qu’un corps, d’aucuns choisissent d’exhiber sans la résoudre la cacophonie des discours et symboles par des références explicites ou non aux hypotextes et métarécits de l’enfance, faisant du vide brouillé un jeu de lumières.Looking for the figure of the child in contemporary British fiction, one is confronted with the paradox of its omnipresence in discourse, matched only by an equally ostentatious physical evanescence. In McEwan’s The Child in Time, the child of the title is gone before the narrative has even begun, while Ishiguro’s When We Were Orphans veils it in confusing layers of fallacious memories, and Byatt’s The Children’s Book stages the slow shedding of its young protagonists’ substance, as their mother gradually turns them into a work of fiction. This very particular kind of absence-cum-presence, which imbues the child with a unique lightness of being, seems to have mesmerized contemporary writers. Exploiting the poetic resources of the strangely non-verbal (infans) literary tool, they strive to prise open a figure so alien to the grown-up writer, and one that is such a challenge to transparency, that it invariably leads them to write instead about the impossibility of mimetic art, about fakes, about trompe-l’oeil fiction. For all its apparent poetic opacity, the child is indeed transparent in more ways than one: defined by centuries of literature as an ideally blank space of non-being, the innocent infant has become a repository for all adult values, a self-cancelling sign both opaque in meaning and see-through in substance which several contemporary novelists are now trying to liberate from semiotic alienation by sullying it. To have a visible body again, the child must become a poetic monster; for Peter to finally cast a shadow, the chimerical nature of its body – a composite of alien symbolic and discursive fragments – must be exhibited for the palimpsestic mess that it is

Helping Teachers Generate Exercises with Random Coefficients

International audienceFirst, we propose two taxonomies concerning software designed for teaching mathematics, which we call TEL (Technology Enhanced Learning) environment, the first one is on teacher's place and role in TEL environments, the other one is on the activities which are foreseen and provided by TEL environments. Second, we consider TEL environments which provide teachers with tools for building patterns of exercises used in the TEL environment to generate randomly and dynamically exercises or list of exercises. Our approach is compared to classical approaches (based on standards like IMS-QTI or on Computer Algebra Systems)