Sensitivity analysis and parameter estimation for distributed hydrological modeling: potential of variational methods

Variational methods are widely used for the analysis and control of computationally intensive spatially distributed systems. In particular, the adjoint state method enables a very efficient calculation of the derivatives of an objective function (response function to be analysed or cost function to be optimised) with respect to model inputs. In this contribution, it is shown that the potential of variational methods for distributed catchment scale hydrology should be considered. A distributed flash flood model, coupling kinematic wave overland flow and Green Ampt infiltration, is applied to a small catchment of the Thoré basin and used as a relatively simple (synthetic observations) but didactic application case. It is shown that forward and adjoint sensitivity analysis provide a local but extensive insight on the relation between the assigned model parameters and the simulated hydrological response. Spatially distributed parameter sensitivities can be obtained for a very modest calculation effort (~6 times the computing time of a single model run) and the singular value decomposition (SVD) of the Jacobian matrix provides an interesting perspective for the analysis of the rainfall-runoff relation. For the estimation of model parameters, adjoint-based derivatives were found exceedingly efficient in driving a bound-constrained quasi-Newton algorithm. The reference parameter set is retrieved independently from the optimization initial condition when the very common dimension reduction strategy (i.e. scalar multipliers) is adopted. Furthermore, the sensitivity analysis results suggest that most of the variability in this high-dimensional parameter space can be captured with a few orthogonal directions. A parametrization based on the SVD leading singular vectors was found very promising but should be combined with another regularization strategy in order to prevent overfitting

Physical modeling of bilabial plosives production

International audienceThe context of this study is the physical modeling of speech production. The first step of our approach is to realize in-vivo measurements during the production of the vowel-consonant-vowel sequence /apa/. This measurements concerns intra-oral pressure, acoustic pressure radiated at the lips and labial parameters (aperture and width of the lips) derived from a high-speed video recording of the subject face. In a second time, theoretical models from speech production literature are under investigation to predict the air flow trough the lips. A model is validated by comparing his predictions with results obtained from measurements on a replica of phonatory system. Then, the same experimental set-up is used to introduce an aerodynamic model of supraglottal cavity expansion. Finally, we achieve numerical simulations of a vowel-bilabial plosive-vowel utterance, by using these models. Simulation results highlight the influence of the cheeks expansion during the production of bilabial plosives

Identification of peer effects using group size variation

This paper considers the semiparametric identification of endogenous and exogenous peer effects based on group size variation. We show that Lee (2006)'s linear-in-means model is generically identified, even when all members of the group are not observed. While unnecessary in general, homoskedasticity may be required in special cases to recover all parameters. Extensions to asymmetric responses to peers and binary outcomes are also considered. Once more, most parameters are semiparametrically identified under weak conditions. However, recovering all of them requires more stringent assumptions. Eventually, we bring theoretical evidence that the model is more adapted to small group

Development of new test instruments and protocols for the diagnostic of fuel cell stacks

In the area of fuel cell research, most of the experimental techniques and equipments are still devoted to the analysis of single cells or very short stacks. However, the diagnosis of fuel cell stacks providing significant power levels is a critical aspect to be considered for the integration of fuel cell systems into real applications such as vehicles or stationary gensets. In this article, a new instrument developed in-lab is proposed in order to satisfy the requirements of electrochemical impedance studies to be led on large FC generators made of numerous individual cells. Moreover, new voltammetry protocols dedicated to PEMFC stack analysis are described. They enable for instance the study of membrane permeability and loss of platinum activity inside complete PEMFC assemblies. Keywords: PEMFC; Stack; Characterization; Electrochemical Impedance Spectroscopy; Cyclic Voltammetry; Linear Sweep Voltammetry

Reconstruction 3D du bâti à partir d'une seule image par naissances et morts multiples

National audienceIn this paper, contrary to the classical approach addressing the 3D reconstruction problem as an inverse problem and solving it by matching two images from a stereoscopic pair, we show that we can solve the direct problem in a simpler way. To do so, we randomly propose configurations of buildings while keeping only the most relevant ones, using a multiple births and deaths algorithm. Notably, we show that this approach does not imply a prohibitory computation time, thanks to the freeware OpenGL which exploits the graphic card. The first results show that the proposed approach is relevant. In particular, it allows solving ambiguities for which inverting the problem is almost impossible.Dans cet article, nous nous écartons de l'approche classique qui considère la reconstruction 3D comme un problème inverse et la résout en mettant en correspondance deux images d'une paire stéréoscopique. Au contraire, nous montrons qu'il est plus simple de résoudre le problème direct. Pour ce faire, nous proposons aléatoirement des configurations de bâtiments pour ne conserver que les plus pertinentes par un algorithme de type naissances et morts multiples. Nous montrons notamment que cette approche ne nécessite pas un temps de calcul prohibitif, grâce à la puissance de calcul d'OpenGL qui s'appuie sur la carte graphique. Les premiers résultats obtenus montrent la pertinence de l'approche adoptée. En particulier, elle permet de résoudre des ambiguïtés pour lesquelles l'inversion du problème serait quasiment impossible

Formally verified optimizing compilation in ACG-based flight control software

International audienceThis work presents an evaluation of the CompCert formally specified and verified optimizing compiler for the development of DO-178 level A flight control software. First, some fundamental characteristics of flight control software are presented and the case study program is described. Then, the use of CompCert is justified: its main point is to allow optimized code generation by relying on the formal proof of correctness and additional compilation information instead of the current un-optimized generation required to produce predictable assembly code patterns. The evaluation of its performance (measured using WCET and code size) is presented and the results are compared to those obtained with the currently used compiler

Selecting the quality of mule duck fatty liver based on near-infrared spectroscopy

Background: "Foie gras" is produced predominantly in France and about 90% of the commercialized product is obtained from male mule ducks. The melting rate (percentage of fat released during cooking) is the main criterion used to determine the quality of "foie gras". However, up to now the melting rate could not be predicted without causing liver damage, which means that selection programs could not use this criterion. Methods: Fatty liver phenotypes were obtained for a population of over 1400 overfed male mule ducks. The phenotypes were based on two types of near-infrared spectra (on the liver surface and on ground liver) in order to predict the melting rate and liver composition (ash, dry matter, lipid and protein contents). Genetic parameters were computed in multiple traits with a "sire-dam" model and using a Gibbs sampling approach. Results: The estimates for the genetic parameters show that the measured melting rate and the predicted melting rate obtained with two near-infrared spectrometer devices are genetically the same trait: genetic correlations are very high (ranging from +0.89 to +0.97 depending on the mule duck parental line and the spectrometer) and heritabilities are comparable. The predictions based on the spectra of ground liver samples using a laboratory spectrometer correlate with those based on the surface spectra using a portable spectrometer (from +0.83 to +0.95 for dry matter, lipid and protein content) and are particularly high for the melting rate (higher than +0.95). Although less accurate than the predictions obtained using the spectra of ground liver samples, the phenotypic prediction of the melting rate based on surface spectra is sufficiently accurate to be used by "foie gras" processors. Conclusions: Near-infrared spectrometry is an efficient tool to select liver quality in breeding programs because animals can be ranked according to their liver melting rate without damaging their livers. Thus, these original results will help breeders to select ducks based on the liver melting rate, a crucial criterion that defines the quality of the liver and for which there was previously no accurate predictor. (Résumé d'auteur

Towards Formally Verified Optimizing Compilation in Flight Control Software

International audienceThis work presents a preliminary evaluation of the use of the CompCert formally specified and verified optimizing compiler for the development of level A critical flight control software. First, the motivation for choosing CompCert is presented, as well as the requirements and constraints for safety-critical avionics software. The main point is to allow optimized code generation by relying on the formal proof of correctness instead of the current un-optimized generation required to produce assembly code structurally similar to the algorithmic language (and even the initial models) source code. The evaluation of its performance (measured using WCET) is presented and the results are compared to those obtained with the currently used compiler. Finally, the paper discusses verification and certification issues that are raised when one seeks to use CompCert for the development of such critical software

PROTEUS – Creating Distributed Maintenance Systems through an Integration Platform

International audienceThis paper is based on the results from the project PROTEUS sponsored by the French Ministry of Economy, Finance and Industry and the Federal Ministry of Education and Research of Germany under the label of European Commission Initiative ITEA. It presents the architecture and the basic concepts of an integration platform, which constitutes the framework of systems implementing the tasks dedicated to remote maintenance, as well as other applications, for large and medium scale industrial installation. The approach illustrated here is useful for executing any maintenance strategy by implementing the relevant means for controlling workflow between several system components as well as the component's integration itself. The paper first points out the need for designing such a maintenance-oriented platform, continues with a requirements analysis to a global maintenance system followed by the description of the fundamentals of a maintenance application integration system. Finally a sample implementation of a maintenance scenario is given