Research on vicarious reinforcement has answered many questions but whether vicarious reinforcement increases the likelihood that an observer will imitate a model, a social learning theory would predict, or sets the occasion for the observer to perform an alternate response, as a discriminative stimulus interpretation of vicarious reinforcement suggests, seems to depend on (1) the setting, (2) procedure, and (3) reinforcers used. In an effort to better understand the function of vicarious reinforcement, while controlling for subjects; histories and using tangible reinforcers, 47 preschool children participated in two experiments that (1) provided an experimental history of responding on several levers, (2) provided differential reinforcement on the levers during training, and (3) assessed the effects of observing a model respond on a lever and receive tokens. In Experiment I, 18 subjects who were trained to respond on three levers responded during an extinction period and then observed either an adult model respond on a fourth, novel lever or observed a control procedure. Only subjects who observed the model receive tokens responded on the same lever as the model during an additional extinction period. The extinction period was procedurally defined and relatively short in duration. The results of Experiment I supported social learning theory; however, imitation effects were short lived. Another experiment was conducted to evaluate more fully the extinction of the modeled behavior found in Experiment I. In Experiment II, 29 subjects who were trained to respond on three levers responded during an extinction period and then observed an adult model in one of four modeling conditions. The subjects in this experiment were exposed to the model lever during training and had an extensive history of never being reinforced on the modeled lever. Only some of the subjects who observed the model receive tokens responded on the model lever and only for a short period of time. The results of this experiment illustrated the importance of the reinforcement history of the observer and supported previous studied which found an extinction effect for vicarious reinforcement. Taken together, these experiments illustrate the limits of social learning theory because imitation effects were short lived and suggest certain procedures that will enhance the use of vicarious reinforcement in applied setting.

The nonlinearities of a nonlinear system can degrade the performance of a closed-loop system. In order to improve the performance of the closed-loop system, an adaptive technique, using a neural network, was developed. A neural network is placed in series between the output of the fixed-gain controller and the input into the plant. The weights are initialized to values that result in a unity gain across the neural network, which is referred to as a "feed-through neural network." The initial unity gain causes the output of the neural network to be equal to the input of neural network at the beginning of the convergence process. The result is that the closed-loop system's performance with the neural network is, initially, equal to the closed-loop system's performance without the neural network. As the weights of the neural network converge, the performance of the system improves. However, the back propagation algorithm was developed to update the weights of the feed-forward neural network in the open loop. Although the back propagation algorithm converged the weights in the closed loop, it worked very slowly. Two new update algorithms were developed for converging the weights of the neural network inside the closed-loop. The first algorithm was developed to make the convergence process independent of the plants dynamics and to correct for the effects of the closed loop. The second algorithm does not eliminate the effects of the plant's dynamics, but still does correct for the effects of the closed loop. Both algorithms are effective in converging the weights much faster than the back propagation algorithm. All of the update algorithms have been shown to work effectively on stable and unstable nonlinear plants. / Ph. D.

No description available.

L’exploitation des traces d’interaction lors de tâches d’apprentissage permet différents types de retour d’expérience : retour immédiat pour l’apprenant sur sa tâche, retour d’expérience au niveau d’un groupe de pairs, retour d’expérience vers le tuteur en situation d’apprentissage, retour d’expérience vers les concepteurs de formation. Ces retours d’expérience s’expriment le plus souvent sous une forme synthétique : des indicateurs. Ce travaille apporte des solutions originales aux deux facettes indispensables à toute ingénierie des indicateurs : 1) intégration d’un système à base de traces comme nouvelle brique disponible pour la conception d’EIAH (intégration dans un framework de type Moodle) ; 2) Elaboration d’un processus intégré de transformations explicites de traces modélisées préparant à un calcul explicite d’indicateurs. Les connaissances de modélisation des traces, des transformations et de la description de la formule d’indicateur sont capitalisées, facilitant la réutilisation et la constitution de bibliothèques d’indicateurs « prêts à l’emploi ». Pour illustrer l’approche, nous avons développé un jeu de modèles de traces et de transformations adaptées à une situation cible choisie pour sa richesse interactive. Ce jeu de modèles pourra concerner l’apprenant seul, mais aussi le groupe de pairs et éventuellement le groupe classe pour révéler certains phénomènes, tels que la collaboration, non visibles au niveau de l’individu seul. L’outil développé, pour faire la démonstration de l’approche proposée, a été testé en vraie grandeur sur plusieurs terrains universitaires et est disponible en téléchargement pour Moodle. / The exploitation of user’s interaction historic provides different level of experience’s feedback and for different kind of users: experience feedback for teachers, student, group of students, TEL designers. This work provides novel solutions to two essential aspects to any engineering indicators: 1) Integration of a Trace Based System as a new component for TEL systems design (integration in a framework as Moodle for example); 2) Building a set of Trace models with a transformations process to compute explicitly indicators. Knowledge modeling traces, transformations, and indicators’ formula description are capitalized, allowing the reuse and the creation of indicators library “ready to use” To illustrate the approach, we have developed a set of traces models and transformations adapted to a chosen learning situation. This set of models will involve him- self, the peers group and possibly the whole class to reveal some phenomena, such as collaboration. A demonstration software has been developed and tested in three different university contexts and is available for download for Moodle.

No description available.

L’objectif de ma thèse est de mieux comprendre le fonctionnement de deux proxies de température de surface de l’océan (SST), les indices Uk’37 et TEX86, notamment en terme de saison et de profondeur de production des alcènones et des tétraéthers sur lesquels ils reposent, au cours des 160 000 dernières années au niveau de la marge ibérique. L’originalité de ce projet de thèse réside dans sa double approche, avec d’une part l’acquisition des enregistrements sédimentaires, et d’autre part l’utilisation d’un outil de modélisation régionale couplée physique-biogéochimie pour simuler ces proxies sous 3 modes climatiques : au présent, lors du dernier maximum glaciaire, et lors d’événements de Heinrich. La confrontation des résultats des biomarqueurs avec ceux de tests de scénarios de production par la modélisation ont conduit aux conclusions suivantes. L’Uk’37 enregistre bien des SSTs moyennes annuelles, alors que le TEX86 présente a priori des températures beaucoup trop élevées pour cette zone. La formulation d’une calibration régionale pour le TEX86 permet d’obtenir des SSTs moyennes annuelles cohérentes. Le meilleur endroit de la marge ibérique pour appliquer ces deux paléothermomètres est le site de Shackleton. Après analyse fine des timings des signaux multiproxies, le TEX86 semble être produit à des profondeurs intermédiaires, potentiellement par des communautés d’Archées d’origine méditerranéenne. Les variations de gradients thermiques latitudinaux ont été quantifiées, et des réorganisations de masses d’eaux de surface et intermédiaire au niveau de la marge ibérique ont été envisagées selon le climat glaciaire/interglaciaire lors des évènements de type Heinrich. / My PhD project aims at better understanding the functioning of both organic proxies of sea surface temperature (SST), Uk’37 and TEX86, especially in terms of season and depth of alkenone and tetraether production, over the last 160 000 years on the Iberian Margin. The originality of this project lies in its double approach: on the one hand, with the acquisition of Uk’37 and TEX86 sedimentary records from the Iberian Margin, and on the other hand with the use of a coupled physics-biogeochemistry regional model to simulate these temperature proxies for 3 climate modes: at present, during the last glacial maximum, and during Heinrich Stadials. The comparison of biomarker results with those from modeling tests of production scenarios provided the following conclusions. Uk’37 does record annual mean SSTs, whereas TEX86 shows a priori too high temperature for this area. The formulation of a regional calibration for TEX86 index enables to obtain coherent past annual mean SSTs. The best location to apply both paleothermometers on the Iberian Margin is the Shackleton site. After refined analysis of multiproxy signal timings, TEX86 production seems to take place at intermediate depth, potentially by archaean communities coming from the Mediterranean Sea. Latitudinal thermal gradient variations are quantified, and glacial/interglacial surface and intermediate water masses reorganizations during 'Heinrich like' events are considered.

Sandstorms are frequently accompanied by intense electric fields and lightning. In a very narrow region close to the ground, sand particles undergo a charge exchange during which larger-sized sand grains become positively charged and smaller-sized sand grains become negatively charged and then all particles become suspended by the turbulent fluid motion. Although the association of intense electric fields with sandstorms has long been observed, the mechanism that causes these intense electric fields has not yet been described. Here, we hypothesize that differently sized sand particles are differentially transported by turbulence in the flow, resulting in a large-scale charge separation and a consequential large-scale electric field. To confirm our hypothesis, we combined a large-eddy simulation framework comprising a turbulent atmospheric boundary layer and movement of sand particles with an electrostatic Gauss law to investigate the physics of the electric fields in sandstorms. We varied the strength of the sandstorm from weak to strong as parametrized by the number density of the entrained sand particles. Our simulations reproduced observational measurements of both mean and root mean squared fluctuation values of the electric field. Our results allowed us to propose a law in which the electric field scales to two-thirds of the power of the concentration of the sand particles in weak-to-medium strength sandstorms. The underlying approach to simulate the solid particle-laden flow is Eulerian-Eulerian in which the particles are characterized by statistical descriptors. To explore the essential physics of the electric field generation in a sandstorm, we model the high-Reynolds-number atmospheric boundary-layer (ABL) using two different canonical turbulent flows: one model is that of a turbulent boundary-layer (TBL), and the second one is that of a turbulent half-channel flow. For the particle phase, the direct quadrature method of moments (DQMOM) is chosen in which the abscissas and weights of the quadrature method are tracked directly. The utilization of this framework is proposed to examine the transport of sand in sandstorms. Furthermore, the physical mechanisms necessary for production and sustenance of large-scale electric fields in sandstorms is investigated.

No description available.

Large Eddy Simulation (LES) is a relatively more accurate and reliable alternative to solution of Reynolds Averaged Navier Stokes (RANS) equations in simulating complex turbulent flows at a lesser computational cost than a direct numerical simulation (DNS). However, LES of wall-bounded flows still requires a very high grid resolution in the inner wall layer making its widespread use difficult. Different attempts have been made in the past time to overcome this problem by modeling the near wall turbulence instead of resolving it. One such approach is a two-layer wall model that solves for a reduced one-dimensional equation in the inner wall layer, while solving for the filtered Navier-Stokes equations in the outer layer. The use of such a model allows for a coarser grid resolution than a wall resolved LES. This work validates the performance of a two-layer wall model developed for an arbitrary body fitted non-orthogonal grid in the flow over a wall mounted hump at Reynolds number 9.36x105. The wall modeled large eddy simulation (WMLES) relaxes the grid requirement compared to a wall resolved LES (WRLES) by allowing the first off-wall grid point to be placed at a y+ of approximately 20-40. It is found that the WMLES results are general good agreement with WRLES and experiments. Surface pressure coefficient, skin friction, mean velocity profiles, and the reattachment location compare very well with experiment. The WMLES and WRLES exhibit some under prediction of the peak values in the turbulent quantities close to the reattachment location, with better agreement with the experiment in the separated region. In contrast, a simulation that did not employ the wall model on the grid used for WMLES failed to predict flow separation and showed large discrepancies with the experimental data. In addition to the relaxation of the grid requirement in the wall normal direction, it was also observed that the wall model allowed a reduction in the number of computational cells in the span-wise direction by half. However an LES calculation on a grid with reduced number of cells in span-wise direction turned unstable almost immediately, thereby highlighting the effectiveness of the wall model. Besides reducing the number of grid points in the spatial domain, the relaxed grid resolution for the WMLES also permitted the use of a larger time step. This resulted in an order of magnitude reduction in the total CPU time relative to WRLES. / Master of Science

Abstract : Electroencephalography (EEG) is a non-invasive neuroimaging modality that was first introduced over 80 years ago. Surface EEG does not directly measure neuronal activity, and it is often assumed that it cannot provide indications on the underlying neuronal firing. However, recent studies based on invasive measurements in monkeys have shown that the coupling between two EEG frequency bands, namely the Gamma (25-45 Hz) and Delta (2-4 Hz) bands, is a good predictor of underlying mass-spiking activity. Specifically, when the Delta signal is in its trough and Gamma power is high, the probability of mass- firing of neurons is large. Here, we investigate this property in healthy human EEG acquired during resting-state. Using the interaction between Delta phase and Gamma power, we derived a modeled spike signal (MSS) from the recorded EEG. We found the power spectrum density (PSD) pattern of the MSS to be similar to that observed in animal studies. Specifically, between 1-10 Hz that the PSD deviates from a 1/[florin] trend and exhibits a small peak at about 2-3Hz. In addition, an inter-hemispheric correlation was found between the MSS of the different pairs of electrode in opposite hemispheres. Our results open the possibility of studying underlying neuronal output with non-invasive EEG. // Résumé : L'électroencéphalographie (EEG) est une modalité de neuro-imagerie non invasive qui a été introduite il y a plus de 80 ans. L’EEG de surface ne mesure pas directement l’activité neuronale et il est généralement supposé qu’elle ne donne pas d’indications sur la décharge neuronale sous-jacente. Cependant des études récentes ont montré à l’aide de mesures invasives que le couplage entre deux bandes de fréquences EEG, soit les bandes Gamma (25-45 Hz) et Delta (2-4 Hz), est un bon indicateur de l’activité neuronale de masse sous-jacente chez les singes. Plus précisément, lorsque le signal Delta est dans un creux (phase de π) et que la puissance dans le signal Gamma est élevée, la probabilité de décharge de masse des neurones est grande. Cette propriété est ici étudiée dans les signaux EEG d’humains sains en état de repos. En se basant sur l'interaction entre la phase du signal Delta et la puissance du signal Gamma, nous avons dérivé un modèle de l’activité neuronale de masse sous-jacente (modeled spike signal-MSS) obtenu à partir du signal l'EEG enregistrée. On trouve que la densité spectrale de puissance (power spectal density-PSD) du MSS est similaire à celle observée dans les études animales. Plus spécifiquement, entre 1-10 Hz la PSD s’écarte d’une tendance en 1 / [florin] et présente un pic de faible amplitude à environ 2-3Hz. En outre, une corrélation inter-hémisphérique a été observée entre les MSS de différentes paires d'électrodes positionnées sur les hémisphères opposés. Nos résultats ouvrent la possibilité d'étudier l’activité neuronale sous-jacente par EEG non-invasive.