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Empirical studies within a cognitive load framework have determined that for novice learners, worked examples provide appropriate levels of instructional guidance. As learners advance in specific subject domains, worked examples should be gradually replaced by practice problems with limited guidance. These studies compared immediate and delayed performance in transfer from examples to practice problems using example-problems pairs and gradual fixed fading of worked examples as well as a control condition of pure problem solving. These studies were conducted with employees of a financial services company in a classroom environment. In Experiments 1 and 2, the fading condition indicated possible benefits over the other conditions on immediate and delayed performance measures (although results were not statistically significant). Experiment 3 used a modified fading method and demonstrated that the fading condition performed marginally better than the problem solving condition on delayed performance measures (although results were not statistically significant). Even though the fading condition did not demonstrate significant advantages in immediate post-test measures, over time learners benefited most from this condition. Experiment 4 investigated if the delayed fading effect found in experiment 3 would be observed using far transfer test performance measures. The results of this experiment indicated that the fading condition performed marginally better than the problem solving condition on delayed transfer post-test performance (although results were not statistically significant). Generally the results of this thesis favored the fading condition over the example-problem and problem solving conditions, and the advantage of this condition was enhanced with greater performance in delayed and transfer post-test measures.

We consider the inverse source problem arising in thermo-and photoacoustic tomography. It consists in reconstructing the initial pressure from the boundary measurements of the acoustic wave. Our goal is to extend versatile time reversal techniques to the case when the boundary of the domain is perfectly reflecting, effectively turning the domain into a reverberant cavity. Standard time reversal works only if the solution of the direct problem decays in time, which does not happen in the setup we consider. We thus propose a novel time reversal technique with a nonstandard boundary condition. The error induced by this time reversal technique satisfies the wave equation with a dissipative boundary condition and, therefore, decays in time. For larger measurement times, this method yields a close approximation; for smaller times, the first approximation can be iteratively refined, resulting in a convergent Neumann series for the approximation.

The work deals with the rearing of brown trout (Salmo trutta m farion) under controlled conditions. For this study was use intensive hatching metods. We observed and recorded stocking density and her influences an growth, survival in controlled conditions in fish hatchery in Kaplice Ltd

Dans cette thèse nous considérons l’équation des ondes amorties vectorielle sur une variété riemannienne compacte, lisse et sans bord. L’amortisseur est ici une fonction lisse allant de la variété dans l’espace des matrices hermitiennes de taille n. Les solutions de cette équation sont donc à valeurs vectorielles. Nous commençons dans un premier temps par calculer le meilleur taux de décroissance exponentiel de l’énergie en fonction du terme d’amortissement. Ceci nous permet d’obtenir une condition nécessaire et suffisante la stabilisation forte de l’équation des ondes amorties vectorielle. Nous mettons aussi en évidence l’apparition d’un phénomène de sur-amortissement haute fréquence qui n’existait pas dans le cas scalaire. Dans un second temps nous nous intéressons à la répartition asymptotique des fréquences propres de l’équation des ondes amorties vectorielle. Nous démontrons que, à un sous ensemble de densité nulle près, l’ensemble des fréquences propres est contenu dans une bande parallèle à l’axe imaginaire. La largeur de cette bande est déterminée par les exposants de Lyapunov d’un système dynamique défini à partir du coefficient d’amortissement. / In this thesis we are considering the vectorial damped wave equation on a compact and smooth Riemannian manifold without boundary. The damping term is a smooth function from the manifold to the space of Hermitian matrices of size n. The solutions of this équation are thus vectorial. We start by computing the best exponential energy decay rate of the solutions in terms of the damping term. This allows us to deduce a sufficient and necessary condition for strong stabilization of the vectorial damped wave equation. We also show the appearance of a new phenomenon of high-frequency overdamping that did not exists in the scalar case. In the second half of the thesis we look at the asymptotic distribution of eigenfrequencies of the vectorial damped wave equation. Were show that, up to a null density subset, all the eigenfrequencies are in a strip parallel to the imaginary axis. The width of this strip is determined by the Lyapunov exponents of a dynamical system defined from the damping term.