The Informational Approach to Global Optimization in presence of very noisy evaluation results. Application to the optimization of renewable energy integration strategies

We consider the problem of global optimization of a function f from very noisy evaluations. We adopt a Bayesian sequential approach: evaluation points are chosen so as to reduce the uncertainty about the position of the global optimum of f, as measured by the entropy of the corresponding random variable (Informational Approach to Global Optimization, Villemonteix et al., 2009). When evaluations are very noisy, the error coming from the estimation of the entropy using conditional simulations becomes non negligible compared to its variations on the input domain. We propose a solution to this problem by choosing evaluation points as if several evaluations were going to be made at these points. The method is applied to the optimization of a strategy for the integration of renewable energies into an electrical distribution network

La poursuite auditive du mouvement acoustique vers l'acquisition des catégories phonétiques

Cette thèse explore le développement de la parole chez l'enfant durant la première année de vie. Elle vise précisément à caractériser le mécanisme à la base de l'acquisition des catégories phonétiques. Les nombreuses recherches dans le domaine offrent un portrait compréhensible de la trajectoire développementale de la perception de la parole. Les mécanismes de ce développement demeurent toutefois mal compris, particulièrement en ce qui a trait aux stratégies de l'enfant pour faire face au problème de la variabilité. En s'inspirant des théories de l'invariance chez l'adulte et sur la base de données empiriques chez l'enfant, cette thèse présente trois études visant à soutenir l'hypothèse selon laquelle la poursuite auditive du mouvement acoustique sous-tend l'acquisition des catégories phonétiques. Tout d'abord, deux études de modélisation simulent l'acquisition d'un type particulier de catégories phonétiques, les tons lexicaux, par le biais de réseaux neuronaux artificiels de type non supervisé. Ces simulations évaluent l'impact de diverses sources de variabilité et l'efficacité du mouvement acoustique sur la catégorisation des tons en chinois mandarin. Les résultats montrent que malgré un degré modéré de variabilité, les patrons de fréquence fondamentale présentent des régularités permettant de distinguer les quatre tons mandarins, sans information préalable quant au nombre de catégories à découvrir. Ceci suggère que le signal acoustique continu peut suffire à l'acquisition des tons lexicaux, sans besoin de faire appel à un ensemble de propriétés phonétiques abstraites. En présence de multiples sources de variabilité cependant, l'information spectrale du signal de surface n'entretient qu'une faible relation avec les sons de la parole recherchés. À l'opposé, l'information dynamique (les profils de vélocité de la fréquence fondamentale) permet d'atteindre un niveau de performance comparable à celui de l'adulte pour l'identification des tons. De plus, les quatre profils de vélocité découverts par le réseau neuronal correspondent aux quatre tons mandarins et permettent de caractériser les gestes invariants impliqués dans la production tonale. Afin de vérifier si l'enfant peut faire usage de cette stratégie dynamique pour normaliser le signal de la parole, une étude comportementale examine ensuite la capacité d'enfants préverbaux à percevoir des variations acoustiques reflétant une contrainte articulatoire. Une procédure de regard préférentiel est utilisée afin de vérifier si des enfants de 4 et 8 mois peuvent distinguer entre eux des patrons d'intonation possibles et impossibles sur le plan articulatoire et produits par un locuteur inconnu. Les résultats montrent que les enfants des deux groupes d'âge écoutent plus longuement les stimuli possibles, indiquant qu'ils peuvent détecter des variations subtiles de vélocité de la fréquence fondamentale et préfèrent les variations qui respectent la contrainte articulatoire. Ces résultats suggèrent qu'en bas âge déjà, les enfants peuvent calculer la première dérivée d'informations spectrales continues et réduire la variabilité interlocuteur à partir de la dynamique du signal acoustique. Le modèle proposé par les études de simulations permet d'établir l'efficacité de l'information dynamique dans le développement phonétique. L'étude comportementale permet pour sa part de vérifier la sensibilité à cette information chez l'enfant en bas âge. Ces résultats suggèrent que l'invariance se situe à la fois au niveau acoustique/auditif, moteur et développemental, et que la poursuite auditive du mouvement acoustique reflétant les gestes articulatoires représente une stratégie efficace pour l'acquisition des catégories phonétiques. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Catégories phonétiques, Apprentissage distributionnel, Perception de la parole, Production de la parole, Acquisition du langage, Réseaux neuronaux artificiels non-supervisé

Simulating rhizodeposition as a function of shoot and root interactions within a new 3D Functional-Structural Plant Model

Introduction - Rhizodeposition, i.e. the release of organic materials by roots, represents a significant portion of plant's carbon (C) budget, ranging from 5% to 15% of net photosynthesized C (Pausch and Kuzyakov, 2018). Various rhizodeposits can be released by roots, e.g. soluble exudates, secreted mucilage, sloughed cells, or volatile organic compounds. Despite their short lifetime, some of these products have been shown to favor plant growth, e.g. by increasing water and nutrient uptake. Among rhizodeposition processes, exudation has been suggested to depend on the concentration of carbohydrates inside the roots (Personeni et al., 2007). However, rhizodeposition not only depends on the availability of C in the roots, but also on the architecture of the root system, and many have shown that rhizodeposits are more concentrated in specific areas, such as root tips. Consequently, a Functional-Structural Plant Model (FSPM) would theoretically represent the best framework for simulating the spatial and temporal dynamics of rhizodeposition, as it can describe the evolution of both the metabolism and the architecture of the plant. The objective of this work is to create such a framework by coupling a whole-plant FSPM, a 3D root architectural model, and a new model simulating rhizodeposition. Modelling approach - Our strategy has been to combine the FSPM CN-Wheat (Barillot et al., 2016), which describes the main processes of C and nitrogen (N) acquisition and transformation by an individual wheat plant and the 3D growth and development of its aerial organs, with the model ArchiSimple (Pagès et al., 2014) that simulates the development of the 3D root architecture for a range of plant species, and the new model RhizoDep, which calculates a full C balance in each part of a root system in order to simulate local rhizodeposition fluxes. The complementarity of the three models is illustrated in Figure 1: i) CN-Wheat is used to calculate the amount of C allocated from the shoots to the roots, ii) ArchiSimple provides the 3D structure of the root system, and iii) RhizoDep distributes the C provided by the shoots within the 3D root system and simulates the actual growth, respiration and rhizodeposition of each root element based on C availability. The major link between the three models lies in the exchange of C between aboveground and belowground tissues, which is driven by gradients of sucrose concentration in the different compartments of the plant. Preliminary results & short-term perspectives - The coupling of the three models has been started using the OpenAlea platform and its Multiscale Tree Graph formalism (Pradal et al., 2008). First simulations were done using the allocation of C to the roots simulated by CN-Wheat as an input to the root model based on the effective coupling of ArchiSimple and RhizoDep. These simulations show how rhizodeposition is intrinsically dependent on the architecture of the root system and on the total amount of available C. For completing the coupling, several issues still need to be tackled, e.g. how N uptake and metabolism should be spatialized in a 3D root system, how it may be regulated by local C and N availability, and how rhizodeposition can modify soil N availability. However, this modelling approach has already led to a first prototype able to simulate rhizodeposition processes on a dynamic, 3D root system that is fully integrated within the functioning of the whole plant. Its refinement will offer unique opportunities to study the possible link between rhizodeposition and the environmental factors affecting plant growth, e.g. atmospheric CO2 concentration or soil N availability

Impact of the form of a trailer on its aerodynamic performance

Today, energy efficiency is a topic of great importance not only due to limited energy resources, but also their impact on environment. In the case of vehicles, great effort is being spent on reducing weight and making the form more and more aerodynamic to reduce fuel consumption and increase energy efficiency. However, there is a limit to this form because a vehicle should never lose traction. A highly aerodynamic form reduces the downward force which provides the vehicle its traction. A trailer with a highly aerodynamic form was investigated to determine if it would lose traction at different speeds and under different wind conditions. Simulations were carried out using the CFD commercial code ANSYS CFX to determine the flow field and the forces (lift, drag, downward force, etc.) around the trailer. The calculation domain was taken large enough not to affect the flow field. The partial differential turbulent flow equations (continuity, momentum, and turbulence equations) were solved in three dimensions to find the velocity and pressure distributions. Different trailer forms were also investigated. The type of vehicle towing the trailer also has an impact on the flow field around it. Thus, different types of vehicles were considered in the simulations. The results demonstrated that certain forms could cause the loss of traction at high enough speeds. In this article, the model is explained, and the results of a number of cases are presented and discussed

Common Path swept-source OCT interferometer with artifact removal

Peer reviewed: YesNRC publication: Ye

Artifacts removal with a piezoelectric fiber stretcher in Fourier domain OCT

Peer reviewed: YesNRC publication: Ye

Hazard Ratio and Hazard Index as Preliminary Estimators Associated to the Presence of Furans and Alkylfurans in Belgian Foodstuffs.

peer reviewedThis paper provides an estimation of the hazard related to the presence of furan and five alkyl furans (2- and 3-methylfuran, 2-ethylfuran, 2,5- and 2,3-dimethylfuran) in foodstuffs available in the Belgian market. To achieve this objective, a specific sampling plan was designed to ensure that the samples collected (n = 1003) represent the diversity of the Belgian food chain. Herein, the concepts of the Hazard Ratio of a sample (HRs) and the Hazard Index of a sample (HIs) were introduced to primarily characterize the hazard related to the co-occurrence of these compounds. The HRs was measured as the ratio of the potential daily exposure to a substance (expressed in mg/Kg of food) to both the 10% reference dose level for chronic effects (expressed in mg/(kg b.w*day)) and the human standard weight (expressed in kg). Whereas the HIs is the sum of the HRs of compounds that affect the same target organ/system, a hazard index greater than one indicates a highly contaminated matrix that could induce a hazard. It is an alarm indicating that additional attention should be given to this matrix. This may involve additional analyses to confirm the high level, to identify sources, etc. It is also an alarm for the risk assessor to be very careful with flagged matrices and to avoid combination with other matrices. The HIs highlight a relatively low concern for all foods analyzed (HI median < 1.0) with a relatively higher suspected hazard for coffee drinks (HI median = 0.068, HI max = 0.57). This preliminary estimation of the potential hazard suggests that coffee beverages should be examined in more detail in a full risk assessment and that coffee consumption should be taken with caution given the levels of furan and alkylfurans reported in this study