Un método de paneles para el cálculo de la resistencia de ola en barcos

Presentamos un método de paneles para el cómputo linealizado del flujo potencial con una superficie libre, y el de la curva de resistencia de olas sobre un cuerpo con formas hidronavales en función del número de Fi-oude. Las ecuaciones gobernantes del flujo potencial con una superficie libre son, la ecuación de Laplace para el potencial de velocidad, con condiciones de borde apropiadas, y la condición de superficie libre basada en la ecuación de Bernoulli. Sin embargo, el problema hidrodinámico resulta incompletamente formulado, en el sentido de Birkhoof , porque permite soluciones con ondas de superficie viajeras, que se propagan en ambas direcciones (corriente arriba y corriente abajo), donde las primeras son consideradas como sin significado físico y deben ser descartadas. La unicidad de la solución es recuperada mediante una extensión de la técnica de Dawson2We present a panel method for a linearized computation of the potential flow with a free surface, and the wave-resistance curve over a ship-like body as a function of the F'roude number. The governing equations of the potential flow with a free surface are, the Laplace equation for the velocity potential with appropriate boundary conditions and the free surface condition based on the Bernoulli equation. However, the hydrodynamic problem is incompletely-posed, in the Birkoof'sensel, because allows solutions with trailing waves propagating in both (upstream and downstream) directions, where the first should be considered as non-physical and should be discarded. The unicity of the solution is recovered by means of an extension of the Dawson's technique2.Peer Reviewe

3D simulations of self-propelled, reconstructed jellyfish using vortex methods

We present simulations of the vortex dynamics associated with the self-propelled motion of jellyfish. The geometry is obtained from image segmentation of video recordings from live jellyfish. The numerical simulations are performed using three-dimensional viscous, vortex particle methods with Brinkman penalization to impose the kinematics of the jellyfish motion. We study two types of strokes recorded in the experiment1. The first type (stroke A) produces two vortex rings during the stroke: one outside the bell during the power stroke and one inside the bell during the recovery stroke. The second type (stroke B) produces three vortex rings: one ring during the power stroke and two vortex rings during the recovery stroke. Both strokes propel the jellyfish, with stroke B producing the highest velocity. The speed of the jellyfish scales with the square root of the Reynolds number. The simulations are visualized in a fluid dynamics video.Comment: 1 page, 1 figur

Aqueous Free-Radical Polymerization of Non-Ionized and Fully Ionized Methacrylic Acid

Water-soluble, carboxylic acid monomers are known to exhibit peculiar kinetics when polymerized in aqueous solution. Namely, their free-radical polymerization rate is affected by several parameters such as monomer concentration, ionic strength, and pH. Focusing on methacrylic acid (MAA), even though this monomer has been largely addressed, a systematic investigation of the effects of the above-mentioned parameters on its polymerization rate is missing, in particular in the fully ionized case. In this work, the kinetics of non-ionized and fully ionized MAA are characterized by in-situ nuclear magnetic resonance (NMR). Such accurate monitoring of the reaction rate enables the identification of relevant but substantially different effects of the monomer and electrolyte concentration on polymerization rate in the two ionization cases. For non-ionized MAA, the development of a kinetic model based on literature rate coefficients allows us to nicely simulate the experimental data of conversion versus time at a high monomer concentration. For fully ionized MAA, a novel propagation rate law accounting for the electrostatic interactions is proposed: the corresponding model is capable of predicting reasonably well the electrolyte concentration effect on polymerization rate. Nevertheless, further kinetic information in a wider range of monomer concentrations would be welcome to increase the reliability of the model predictions

Forma simétrica de la condición de contorno absorbente DNL para el problema de la resistencia de ola en barcos

En la ref.' hemos presentado un esquema numérico basado en elementos finitos centrados con condición de contorno absorbente (la cual llamamos DNL, por Discrete Yon-Local) para el problema de la resistencia de ola en barcos. Al no agregar viscosidades numéricas este método da curvas de resistencia en función del Froude mejor definidas y posibilita el cálculo de la resistencia por el balance de flujo de momento a la salida. Sin embargo, debido a la naturaleza de la condición absorbente, el sistema resultante es no simétrico y en principio el sistema lineal resultante presenta ciertas dificultades para la factorización. En este trabajo se describe un método por el cual sólo es necesario factorizar una matriz simétrica y con el mismo ancho de banda que una matriz de elementos finitos típica, con el consecuente ahorro de memoria central (RAM).Peer Reviewe

Coplanar back contacts for thin silicon solar cells

The type of coplanar back contact solar cell described was constructed with interdigitated n(+) and p(+) type regions on the back of the cell, such that both contacts are made on the back with no metallization grid on the front. This cell construction has several potential advantages over conventional cells for space use namely, convenience of interconnects, lower operating temperatures and higher efficiency due to the elimination of grid shadowing. However, the processing is more complex, and the cell is inherently more radiation sensitive. The latter problem can be reduced substantially by making the cells very thin (approximately 50 micrometers). Two types of interdigitated back contact cells are possible, the types being dependent on the character of the front surface. The front surface field cell has a front surface region that is of the same conductivity type as the bulk but is more heavily doped. This creates an electric field at the surface which repels the minority carriers. The tandem junction cell has a front surface region of a conductivity type that is opposite to that of the bulk. The junction thus created floats to open circuit voltage on illumination and injects carriers into the bulk which then can be collected at the rear junction. For space use, the front surface field cell is potentially more radiation resistant than the tandem junction cell because the flow of minority carriers (electrons) into the bulk will be less sensitive to the production of recombination centers, particularly in the space charge region at the front surface

Enhancement of cytosine arabinoside-induced apoptosis in human myeloblastic leukemia cells by NFkB/Rel- specific decoy oligodeoxynucleotides

The activity of NF-kB/Rel nuclear factors is known to inhibit apoptosis in various cell types. We investigated whether the subtraction of NF-kB/Rel activity influenced the response of 11 AML (M1, M2 and M4) patients’ cells to AraC. To this end we used a phosphorothioate double-stranded decoy oligodeoxynucleotide (ODN) carrying the NF-kB/Rel- consensus sequence. Cell incubation with this ODN, but not its mutated (scrambled) form used as a control, resulted in abating the NF-kB/Rel nuclear levels in these cells, as verified by electrophoretic mobility shift assay (EMSA) of cells’ nuclear extracts. We incubated the leukemic cells with AraC (32 or 1 mM), in either the absence or presence of the decoy or the scrambled ODN, and analyzed cell apoptosis. The spontaneous cell apoptosis detectable in the absence of AraC (,25%) was not modulated by the oligonucleotide presence in cell cultures. On the other hand, in 10 of the 11 samples tested, the decoy kB, but not the scrambled ODN significantly (P ,0.01 in a Student’s t test) enhanced cell apoptotic response to AraC. Such an effect was particularly remarkable at low AraC doses (1 mM). These findings indicate that NF-kB/Rel activity influences response to AraC in human primary myeloblastic cells, and suggests that the inhibition of NF-kB/Rel factors can improve the effect of chemotherapy in AM

A investigação enquanto prática de deliberação curricular: o caso do projecto ICR

Este artigo refere-se a um projecto de investigação curricular colaborativa que nasceu da conjugação entre, por um lado, a preocupação de alguns professores do ensino básico com o desinteresse manifestado por determinados alunos em relação à escola e ao currículo e, por outro, o interesse de alguns professores universitários em estudar questões de relevância curricular. Dessa conjugação resultou a assunção de uma dimensão investigativa na prática profissional dos referidos professores do ensino básico, concretizada num projecto de investigação-acção colaborativa conduzido por uma equipa de quatro docentes universitários e dez docentes do ensino básico (todos os ciclos), que têm estudado a problemática do reconhecimento (ou não), por parte dos alunos, da relevância das aprendizagens escolares. A recolha de dados tem sido feita em sucessivos ciclos de investigação-acção, com a duração de um ano escolar cada, principalmente através do registo sistemático de manifestações de desinteresse (por parte dos alunos em relação ao currículo) observadas nas aulas e de entrevistas aos alunos, conduzidas pelos seus professores. Os dados têm sido analisados pelos próprios professores do ensino básico, com o apoio dos docentes universitários, e sujeitos a interpretações individuais e de equipa, sendo essas interpretações inspiradoras de novas estratégias de ensino, que são continuamente monitorizadas e revistas. Os processos já amadurecidos e os resultados já gerados sugerem que, apesar da existência de algumas dificuldades, é possível desenvolver nas escolas do ensino básico práticas de gestão curricular que integrem uma componente de investigação.ABSTRACT: This article describes a project of collaborative research on curriculum, which was created by a team that includes (1) elementary school teachers worried about the lack of interest shown by some of their students with regard to the school and the curriculum, and (2) university professors interested in studying issues of curriculum relevance. This partnership has contributed to an increased use of research in classrooms by those elementary school teachers, through an action research project focused on students’ acknowledgment of the relevance of what they learn in school. Data has been collected in successive cycles of action research, mainly through classroom field notes that provide evidence of given students’ lack of interest with regard to the curriculum, and through interviews conducted by the teachers. Each action research cycle is one school year long. Data have been analyzed by the elementary school teachers, sometimes with support from the university professors, and interpreted both individually and collectively. Such interpretation of data inspires teachers in designing new teaching strategies, which are continuously monitored and reviewed. The processes that have already been consolidated and the results that have already been generated by this project suggest that, despite some difficulties, it is possible to develop curricula in elementary schools in ways that entail research

Language and anxiety: an ethnographic study of international postgraduate students

This paper presents some findings from an ethnographic study of international postgraduate students at a university in the South of England, which involved interviews and participant observation over a twelve-month academic year. One of the major themes that emerged from this research was students’ anxiety over their level of English language. Although all students entered their course with a minimum level of IELTS 6, the majority felt disadvantaged by particularly poor spoken English, and suffered feelings of anxiety, shame and inferiority. Low self-confidence meant that they felt ill-equipped to engage in class discussion and in social interaction which used English as the medium of communication. A common reaction to stress caused by language problems was to retreat into monoethnic communication with students from the same country, further inhibiting progress in language. Whilst some linguistic progress was made by nearly all students during the academic sojourn, the anxiety suffered by students in the initial stage must not be underestimated, and appropriate support systems must be put in place to alleviate their distress

A consideration of the challenges involved in supervising international masters students

This paper explores the challenges facing supervisors of international postgraduate students at the dissertation stage of the masters programme. The central problems of time pressure, language difficulties, a lack of critical analysis and a prevalence of personal problems among international students are discussed. This paper makes recommendations for the improvement of language and critical thinking skills, and questions the future policy of language requirements at HE for international Masters students