50 research outputs found
A theoretical and numerical determination of optimal ship forms based on Michell's wave resistance
We determine the parametric hull of a given volume which minimizes the total
water resistance for a given speed of the ship. The total resistance is the sum
of Michell's wave resistance and of the viscous resistance, approximated by
assuming a constant viscous drag coefficient. We prove that the optimized hull
exists, is unique, symmetric, smooth and that it depends continuously on the
speed. Numerical simulations show the efficiency of the approach, and complete
the theoretical results
Breastfeeding shows a protective trend toward adolescents with higher abdominal adiposity
Objective: The question of whether breastfeeding has a protective effect against the development of overweight or obesity later in life remains controversial, especially during adolescence. The objective was to assess the relationship between breastfeeding and adolescents' body composition.
Methods: The HELENA study is a cross-sectional study involving 3,528 adolescents from 10 European cities. The outcome measures were body weight and height, subscapular skinfolds as well as waist circumferences. Breastfeeding, smoking status, and parental socioeconomic status were assessed by self-administered questionnaires. Dietary intake was recorded using two 24 hour recall surveys. Two adjustment approaches were used: i) covariance analysis adjusted for confounding factors (propensity score adjustment) observed between breastfeeding and body composition parameters (BMI Z-score; sum of skinfolds, waist-to-height ratio). An adjusted quantile regression analysis showed a non-significant trend for a protective effect of breastfeeding toward the highest percentiles of adiposity in boys but not in girls. This is of particular interest with respect to the superiority of the waist-to-height ratio over waist circumference and BMI for detecting cardiometabolic risk factors.
Conclusion: This first European study, including a large set of factors influencing adolescents body composition, showed a non significant trend toward a protective effect of breastfeeding on highest percentiles of adolescent's abdominal adiposity
Pericentric heterochromatin reprogramming by new histone variants during mouse spermiogenesis
During male germ cell postmeiotic maturation, dramatic chromatin reorganization occurs, which is driven by completely unknown mechanisms. For the first time, we describe a specific reprogramming of mouse pericentric heterochromatin. Initiated when histones undergo global acetylation in early elongating spermatids, this process leads to the establishment of new DNA packaging structures organizing the pericentric regions in condensing spermatids. Five new histone variants were discovered, which are expressed in late spermiogenic cells. Two of them, which we named H2AL1 and H2AL2, specifically mark the pericentric regions in condensing spermatids and participate in the formation of new nucleoprotein structures. Moreover, our investigations also suggest that TH2B, an already identified testis-specific H2B variant of unknown function, could provide a platform for the structural transitions accompanying the incorporation of these new histone variants
RĂLE DE L'OCCUPATION DU SOL VIS Ă VIS DE LA MODĂLISATION DES FLUX ENERGĂTIQUES ET HYDRIQUES EN MILIEU URBAIN ET PĂRIURBAIN
National audienceLe projet Rosenhy vise Ă Ă©tudier lâimpact de lâoccupation du sol sur la modĂ©lisation mĂ©tĂ©orologique et hydrologique en termes de flux Ă©nergĂ©tiques et hydriques, en milieu urbain et pĂ©riurbain. Trois sites appartenant aux observatoires français OTHU et ONEVU sont au centre de ce projet. Le quartier urbain hĂ©tĂ©rogĂšne du Pin sec (Nantes), impermĂ©abilisĂ© Ă environ 45%, a fait lâobjet dâune campagne expĂ©rimentale durant le mois de juin 2012, visant Ă estimer les flux de chaleur sensible et latente avec une haute rĂ©solution spatiale et temporelle par rapport aux mesures rĂ©alisĂ©es en continu sur ce site depuis 5 ans. Deux bassins versant pĂ©riurbains (La ChĂ©zine Ă Nantes et lâYzeron Ă Lyon), avec un taux dâimpermĂ©abilisation moins important (environ 10%) mais grandissant depuis plusieurs dĂ©cennies, sont aussi Ă©tudiĂ©s. Ces deux derniers sites bĂ©nĂ©ficient dâun suivi hydromĂ©tĂ©orologique depuis 10 ans pour la ChĂ©zine et 15 ans pour lâYzeron. Sur ces trois sites, diffĂ©rentes sources de donnĂ©es dâoccupation du sol Ă diffĂ©rentes rĂ©solutions sont disponibles :diffĂ©rentes bases de donnĂ©es gĂ©ographiques communĂ©ment utilisĂ©es par la communautĂ© scientifique et les collectivitĂ©s et des donnĂ©es tĂ©lĂ©dĂ©tectĂ©es (multispectrales et hyperspectrales). Lâutilisation de ces donnĂ©es en entrĂ©e de diffĂ©rents modĂšles mĂ©tĂ©orologiques et hydrologiques implique un travail dâanalyse et de classification pour adapter les informations aux besoins des modĂšles. Dans ce projet, les diffĂ©rents modĂšles adaptĂ©s au milieu urbain ou pĂ©rirubain sont Ă©valuĂ©s et amĂ©liorĂ©s. Ainsi, les modĂšles hydrologiques pĂ©rirubains sont en dĂ©veloppement pour prendre en compte les diffĂ©rentes pratiques de gestion des eaux pluviales existantes (noues, toitures vĂ©gĂ©talisĂ©es, ...). Lâutilisation conjointe des donnĂ©es simulĂ©es par les diffĂ©rents modĂšles aidera Ă dĂ©terminer le rĂŽle de la part des surfaces naturelles et artificielles sur les bilans Ă©nergĂ©tique et hydrique en milieu plus ou moins urbanisĂ©. Le milieu pĂ©riurbain Ă©tant en Ă©volution, le projet sâintĂ©ressera aussi Ă des scĂ©narios dâurbanisation prospectifs en regardant dâune part lâimpact de la densification sur les scĂ©narios construits pour lâYzeron lors du projet AVuPUR (ANR-VMCS, 2008-2011) et dâautre part, en rĂ©flĂ©chissant conjointement avec Nantes MĂ©tropole, aux possibles voies dâĂ©volution sur le bassin de la ChĂ©zine
Etude "On bouge, on aime ça" (étude pilote du programme EPODE)
LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF
A theoretical and numerical determination of optimal ship forms based on Michellâs wave resistance
ChouBERT : Pré-entraßnement d'un modÚle de langue française pour le Crowdsensing avec des Tweets dans un contexte phytosanitaire
National audienc
Ătat de la recherche sur les enclos circulaires de lâĂge du Bronze dans la moyenne vallĂ©e de la Scarpe : les sites de Lambres-lez-Douai et de Sin-le-Noble (Nord)
National audienc
La bataille navale d'Actium et le mythe de l'arrĂȘte-nef : l'effet de la bathymĂ©trie
Some misprints corrected with respect to the conference proceedings.International audienceA myth of antiquity is explained with modern science in the context of an ancient naval battle. A legend was invoked by the admiral Pliny the Elder to explain the defeat of Antony and Cleopatra against Octavian at the naval battle of Actium. A fish, called echeneis or remora, is said to have the power to stop ships or to delay their motion by adhering to the hull. Naturalists have since studied how the fish sucking-disk with its typical pattern of parallel striae sticks to its host. Here we show the pattern of the free surface measured in a towing tank in the wake of an ancient galley is similar to the striae pattern of the fish. We have measured the bathymetry at the mouth of the Ambracian Gulf that influenced the physical environment of the battle. The computations demonstrate the increase of wave resistance of a galley as a function of the draft to the water depth ratio in shallow water corresponding to the appearance of a particular wake pattern: the echeneidian free surface pattern