Practical targeted learning from large data sets by survey sampling

We address the practical construction of asymptotic confidence intervals for smooth (i.e., path-wise differentiable), real-valued statistical parameters by targeted learning from independent and identically distributed data in contexts where sample size is so large that it poses computational challenges. We observe some summary measure of all data and select a sub-sample from the complete data set by Poisson rejective sampling with unequal inclusion probabilities based on the summary measures. Targeted learning is carried out from the easier to handle sub-sample. We derive a central limit theorem for the targeted minimum loss estimator (TMLE) which enables the construction of the confidence intervals. The inclusion probabilities can be optimized to reduce the asymptotic variance of the TMLE. We illustrate the procedure with two examples where the parameters of interest are variable importance measures of an exposure (binary or continuous) on an outcome. We also conduct a simulation study and comment on its results. keywords: semiparametric inference; survey sampling; targeted minimum loss estimation (TMLE

Adding boundary conditions on the bed for Telemac-3D simulations

Water Qualit

Development of a Hindcast Wave State Database in Northwest Pacific Ocean

Water Qualit

Towards the simulation of submerged bottom structures with vertical walls using Telemac-3D

Water Qualit

On modeling of thermal embrittlement in PWR steels using the local approach to fracture

International audienceExperiments on Charpy and CT specimens were carried out on one heat of A533B steel under two conditions: (i) as received, and (ii) thermally aged (450°C - 5000h). A shift of the ductile to brittle transition temperature (DBTT) was measured after aging. In both cases SEM observations showed that fracture occurred both by intergranular and transgranular cleavage fracture modes when the materials were tested at sufficiently low temperature. Detailed examinations revealed that intergranular fracture was associated with micro-segregated zones, enriched in carbon and phosphorus. A recent model developed by the authors for predicting the fracture toughness of inhomogeneous materials was applied to describe the large scatter related to the bimodal failure modes observed in both conditions and the DBTT shift after aging. It is shown that thermal aging produces a slight decrease of the critical cleavage stress (due to the crossing of grain boundaries embrittled by phosphorus segregation) and a larger decrease of the critical intergranular fracture stress. The McLean-Guttmann- Militzer model is used to predict the kinetics of segregation during aging. An attempt is made to show how these results can be used to model DBBT variations under in-service conditions

Diffusion in grid turbulence of isotropic macro-particles using a Lagrangian stochastic method: theory and validation.

The prediction of solid bodies transport (such as algae, debris, sediment grains, or corrosion deposits) is a necessary requirement in many industrial or environmental processes. The physical processes involved cover a wide range of processes, from tidal flow to turbulent eddies and particle drag. A stochastic model was therefore developed to link the different scales of the physical processes where it was assumed that the particles are dilute enough that they do not affect the flow or the motion of other particles while being large enough that each particle does not follow exactly the fluid motions (i.e., macro-particles). The stochastic model is built in such a way that it uses Reynolds-averaged fluid properties to predict trajectories of individual particles. This model was then tested using experimental measurements obtained for isotropic particles released in semi-homogeneous turbulence. The turbulent flow was generated using a pair of oscillating grids and was characterized using particle image velocimetry measurements. The trajectories of the particles were measured using a pair of high resolution cameras. The comparison between the experimental data and different numerical models gives satisfactory results

Influence of P and C intergranular segregation during manufacturing and ageing on the fracture toughness of nuclear pressure vessel steels

International audienceMechanical tests on Charpy and CT specimens of a low alloy MnNiMo steel under two conditions, as received and thermally aged, revealed a shift of the ductile to brittle transition temperature. In this paper, an approach based on the combination of local fracture mechanics and segregation kinetics is proposed in order to describe this shift

Using the DRAGFO subroutine to model Tidal Energy Converters in Telemac-2D

Water Qualit

Time domain simulation of a piano. Part 1 : model description.

International audienceThe purpose of this study is the time domain modeling of a piano. We aim at explaining the vibratory and acoustical behavior of the piano, by taking into account the main elements that contribute to sound production. The soundboard is modeled as a bidimensional thick, orthotropic, heterogeneous, frequency dependent damped plate, using Reissner Mindlin equations. The vibroacoustics equations allow the soundboard to radiate into the surrounding air, in which we wish to compute the complete acoustical field around the perfectly rigid rim. The soundboard is also coupled to the strings at the bridge, where they form a slight angle from the horizontal plane. Each string is modeled by a one dimensional damped system of equations, taking into account not only the transversal waves excited by the hammer, but also the stiffness thanks to shear waves, as well as the longitudinal waves arising from geometric nonlinearities. The hammer is given an initial velocity that projects it towards a choir of strings, before being repelled. The interacting force is a nonlinear function of the hammer compression. The final piano model is a coupled system of partial differential equations, each of them exhibiting specific difficulties (nonlinear nature of the string system of equations, frequency dependent damping of the soundboard, great number of unknowns required for the acoustic propagation), in addition to couplings' inherent difficulties