Vortical and Wave Modes in 3D Rotating Stratified Flows: Random Large Scale Forcing

Utilizing an eigenfunction decomposition, we study the growth and spectra of energy in the vortical and wave modes of a 3D rotating stratified fluid as a function of $\epsilon = f/N$. Working in regimes characterized by moderate Burger numbers, i.e. $Bu = 1/\epsilon^2 < 1$ or $Bu \ge 1$, our results indicate profound change in the character of vortical and wave mode interactions with respect to $Bu = 1$. As with the reference state of $\epsilon=1$, for $\epsilon < 1$ the wave mode energy saturates quite quickly and the ensuing forward cascade continues to act as an efficient means of dissipating ageostrophic energy. Further, these saturated spectra steepen as $\epsilon$ decreases: we see a shift from $k^{-1}$ to $k^{-5/3}$ scaling for $k_f < k < k_d$ (where $k_f$ and $k_d$ are the forcing and dissipation scales, respectively). On the other hand, when $\epsilon > 1$ the wave mode energy never saturates and comes to dominate the total energy in the system. In fact, in a sense the wave modes behave in an asymmetric manner about $\epsilon = 1$. With regard to the vortical modes, for $\epsilon \le 1$, the signatures of 3D quasigeostrophy are clearly evident. Specifically, we see a $k^{-3}$ scaling for $k_f < k < k_d$ and, in accord with an inverse transfer of energy, the vortical mode energy never saturates but rather increases for all $k < k_f$. In contrast, for $\epsilon > 1$ and increasing, the vortical modes contain a progressively smaller fraction of the total energy indicating that the 3D quasigeostrophic subsystem plays an energetically smaller role in the overall dynamics.Comment: 18 pages, 6 figs. (abbreviated abstract

Freely decaying weak turbulence for sea surface gravity waves

We study numerically the generation of power laws in the framework of weak turbulence theory for surface gravity waves in deep water. Starting from a random wave field, we let the system evolve numerically according to the nonlinear Euler equations for gravity waves in infinitely deep water. In agreement with the theory of Zakharov and Filonenko, we find the formation of a power spectrum characterized by a power law of the form of $|{\bf k}|^{-2.5}$.Comment: 4 pages, 3 figure

Wind generated rogue waves in an annular wave flume

We investigate experimentally the statistical properties of a wind-generated wave field and the spontaneous formation of rogue waves in an annular flume. Unlike many experiments on rogue waves, where waves are mechanically generated, here the wave field is forced naturally by wind as it is in the ocean. What is unique about the present experiment is that the annular geometry of the tank makes waves propagating circularly in an {\it unlimited-fetch} condition. Within this peculiar framework, we discuss the temporal evolution of the statistical properties of the surface elevation. We show that rogue waves and heavy-tail statistics may develop naturally during the growth of the waves just before the wave height reaches a stationary condition. Our results shed new light on the formation of rogue waves in a natural environment

Controlled Transformation of Electrical, Magnetic and Optical Material Properties by Ion Beams

Key circumstance of radical progress for technology of XXI century is the development of a technique which provides controllable producing three-dimensional patterns incorporating regions of nanometer sizes and required physical and chemical properties. Our paper for the first time proposes the method of purposeful direct transformation of the most important substance physical properties, such as electrical, magnetic, optical and others by controllable modification of solid state atomic constitution. The basis of the new technology is discovered by us effect of selective atom removing out of thin di- and polyatomic films by beams of accelerated particles. Potentials of that technique have been investigated and confirmed by our numerous experiments. It has been shown, particularly, that selective atom removing allows to transform in a controllable way insulators into metals, non-magnetics into magnetics, to change radically optical features and some other properties of materials. The opportunity to remove selectively atoms of a certain sort out of solid state compounds is, as such, of great interest in creating technology associated primarily with needs of nanoelectronics as well as many other "nano-problems" of XXI century.Comment: 22 pages, PDF, 9 figure

Radiation hardness qualification of PbWO4 scintillation crystals for the CMS Electromagnetic Calorimeter

This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2010 IOPEnsuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered

Geometric numerical schemes for the KdV equation

Geometric discretizations that preserve certain Hamiltonian structures at the discrete level has been proven to enhance the accuracy of numerical schemes. In particular, numerous symplectic and multi-symplectic schemes have been proposed to solve numerically the celebrated Korteweg-de Vries (KdV) equation. In this work, we show that geometrical schemes are as much robust and accurate as Fourier-type pseudo-spectral methods for computing the long-time KdV dynamics, and thus more suitable to model complex nonlinear wave phenomena.Comment: 22 pages, 14 figures, 74 references. Other author's papers can be downloaded at http://www.lama.univ-savoie.fr/~dutykh

O ensino da leitura e da escrita no 1º ano de escolaridade: os resultados dos alunos em leitura

Tese de Doutoramento em Psicologia Aplicada, Área de especialidade Psicologia EducacionalO presente estudo teve como objetivo caracterizar as práticas de ensino da linguagem escrita em Portugal e perceber o seu impacto na aquisição da leitura no final do 1º ano de escolaridade. A primeira etapa deste estudo correspondeu a um estudo descritivo e comparativo com o realizado por Fijalkow (2003) em França. A partir da resposta a um questionário de 883 professores foi possível verificar que os professores dos dois países se aproximam no que diz respeito aos aspetos metodológicos do ensino da leitura e à avaliação da leitura e da escrita dos alunos. Contudo, os professores portugueses dizem utilizar com maior frequência do que os professores franceses, atividades a partir de livros infantis, outros materiais para além do manual e diferentes propostas de escrita. Na segunda etapa deste estudo, o questionário utilizado foi validado através da sua estrutura fatorial e foram utilizados os fatores revelados para a realização de uma análise hierárquica de clusters. Esta análise revelou três grupos de professores: a) um grupo de professores que centra as suas práticas no ensino do código da linguagem escrita (unidades curtas); b) um grupo que realça a construção de significado na interação com o material escrito (unidades longas); c) e um grupo de professores que reúne nas suas práticas características de ambos os grupos referidos anteriormente (unidades diversificadas). A terceira etapa realizada diz respeito à validação das respostas do questionário através da observação de sala de aula. Foram selecionados 5% dos professores de cada um dos três grupos constituídos (N=42). Cada professor foi observado duas vezes durante 60 minutos em situações escolhidas por si como situações privilegiadas para o ensino da linguagem escrita. Através da utilização de uma grelha de observação que divide as atividades desenvolvidas em atividades que remetem para o código ou para o significado, foi possível confirmar as respostas ao questionário para 55% dos professores participantes. No sentido de perceber o impacto das práticas dos professores na aquisição da leitura dos alunos foram selecionados os professores cujas observações foram coincidentes com as respostas ao questionário e avaliados os seus alunos com recurso a três provas de leitura: leitura de palavras isoladas, decisão lexical e compreensão. Participaram 461 alunos distribuídos pelos três grupos referidos anteriormente. Através da realização de uma MANCOVA, controlando a escolaridade das mães dos alunos, verificou-se que os alunos do grupo unidades diversificadas obtêm melhores resultados em todas as provas do que os alunos dos outros dois grupos. Foi ainda possível constatar que não existiram diferenças de desempenho entre os alunos do grupo unidades curtas e os alunos do grupo unidades longas.ABSTRACT: The present study aimed to characterize the teaching practices of written language and understand its impact on reading acquisition by the end of 1st grade. The first step of this study was a descriptive and comparative study to the one conducted by Fijalkow (2003) in France. Based on questionnaire answers of 883 teachers, we found that teachers from both countries have similar approaches regarding methodological aspects of teaching of reading and students’ assessment of reading and writing abilities. However, Portuguese teachers stated that they use more frequently activities from children's literature, other materials besides the manual and different writing proposals than French teachers. In the second step of the study, the questionnaire was validated through its factorial structure and the factors disclosed were used to perform a hierarchical cluster analysis. This analysis revealed three groups of teachers: a) a group of teachers who focus its practices in teaching the code of written language (short units), b) a group that emphasizes the construction of meaning in interaction with the written material (long units), c) and a group of teachers who gathered in their practices characteristics of both groups mentioned above (diversified units). The third step concerns the validation of the questionnaire answers through classroom observation. 5% of the teachers in each of the three groups were selected (N=42). Each teacher was observed twice during 60 minutes in situations identified by them as privileged situations for teaching written language. Using an observation grid which divides the activities conducted in code-activities or the meaning-activities it was possible to confirm questionnaire answers for 55% of the participating teachers. In order to understand the impact of teachers’ practices in students reading acquisition, teachers whose observations were coincident with the questionnaire answers were selected and their students were evaluated using three reading tests: single words reading, lexical decision task and comprehension task. Participants were 461 students distributed through the three groups previously mentioned. By conducting a MANCOVA, controlling mothers’ education level, we concluded that students in the diversified unit group obtain better results in all reading tests than students from the other groups. It was also possible to confirm that there were no differences in performance between students of the short units group and students of the long units group.Tese de Doutoramento em Psicologia Aplicada, Área de especialidade Psicologia EducacionalApoio financeiro da Fundação para a Ciência e Tecnologia (SFRH/BD/64630/2009