2,075 research outputs found

    Estimation of Effective Elastic Properties of General Multifunctional Honeycomb Structures Using a Unit Cell Method

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    Sandwich composite structures are ideal configurations in which to incorporate additional functionality beyond load carrying capabilities. The inner core can be layered to facilitate other functions such as power storage for a battery. In this work we investigate an assemblage of analytical tools to compute effective properties that allow complex layered core architectures to be homogenized into a single continuum layer. This provides a great increase in computational efficiency to numerically simulate the structural response of multifunctional sandwich structures under applied loads

    The Oral University. Attitudes to music teaching and learning in the Gambia.

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    The present study seeks to examine attitudes to teaching and learning among jalis in the Gambia. Although this is the main focus, the horizon of which the study is carried out, analysed and discussed, is the development of music teacher education in Sweden during the last three decades, and of which I have been a participant. The intention of the study is to expand current views on music teaching and learning so that teachers will be better equipped to work and function in a multicultural society. Specifically, the intention is to open the doors to the Mandinka approach to music education, in order to illuminate their philosophy of music teaching. The research question is: What are the attitudes to music teaching and learning in the Gambia, and in what ways are the jalis experiences of, and attitudes towards music and music education expressed? This study concerns cultural meetings on a number of levels: between people, between institutions and between literal and oral worlds of knowledge. The methodology chosen reflects these meetings: all results stem from the travels that I and my informant and co-researcher jali Alagi Mbye have made visiting musicians in the Gambia and, during a long period, moving in and out of each others cultures. The core of the empirical data consists of observations and interviews with jalis and other Gambian musicians. The emic and the etic perspectives of these interviews are reflected in different ways. In one of the interviews my main informant, jali Alagi Mbye, acts as a co-researcher, thereby opening up new dimensions to the study. In this interview, it is the accompaniment of the 21-stringed kora that leads the conversation, just as much as the questions. Because of the multifaceted content of this interview, the full transcript and a CD-recording is attached in the appendix. The results show that the oral jali tradition is in some respects both structured and formalised. Hence, it is described as ‘the Oral University’. Delving deeper into the conversations with the musicians ‘inside’ and ‘outside’ the jali musical culture, the thematic outcome is differing. While the ‘insiders’ highlight the intellectual dimension of music education expressed in thoughts on culture and identity, and with references to the Sunjata orature, the ‘outsiders’ highlight the practical instrumental training dimension of music education, expressed, for example, by praising ‘the art of not talking’ as a way of teaching, and claiming that the master level and position is reached when people start to dance to your playing. In conclusion, these differences in attitudes to music teaching and learning reflect different ways of expressing knowledge

    Hydrographic Training and Technical Assistance to Developing Countries - Norwegian Assistance to Mozambique

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    Norway has, through the Norwegian Agency for Development Assistance (NORAD), actively supported the Hydrographic organization of the Mozambique government since 1986. At the beginning, the Norwegian Hydrographic Service (NSKV) was brought in, as a consultant, for the first two years, with its own staff in Mozambique, then later, as a backup for a NORAD employed hydrographic surveyor. A new contract, effective from 1st January 1991, has been signed, this time between the Mozambican Organization, which is now called Instituto Nacional de Hidrografia e Navegaçâo (INAHINA) and NSKV. It is funded by NORAD, and NSKV has undertaken to build and develop INAHINA to such an extent that it will be able to continue operations and continue to perform satisfactorily after the withdrawal of NSKV-assistance

    Glance Look Stare

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    Density-Dependence as a Size-Independent Regulatory Mechanism

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    The growth function of populations is central in biomathematics. The main dogma is the existence of density dependence mechanisms, which can be modelled with distinct functional forms that depend on the size of the population. One important class of regulatory functions is the θ\theta-logistic, which generalises the logistic equation. Using this model as a motivation, this paper introduces a simple dynamical reformulation that generalises many growth functions. The reformulation consists of two equations, one for population size, and one for the growth rate. Furthermore, the model shows that although population is density-dependent, the dynamics of the growth rate does not depend either on population size, nor on the carrying capacity. Actually, the growth equation is uncoupled from the population size equation, and the model has only two parameters, a Malthusian parameter ρ\rho and a competition coefficient θ\theta. Distinct sign combinations of these parameters reproduce not only the family of θ\theta-logistics, but also the van Bertalanffy, Gompertz and Potential Growth equations, among other possibilities. It is also shown that, except for two critical points, there is a general size-scaling relation that includes those appearing in the most important allometric theories, including the recently proposed Metabolic Theory of Ecology. With this model, several issues of general interest are discussed such as the growth of animal population, extinctions, cell growth and allometry, and the effect of environment over a population.Comment: 41 Pages, 5 figures Submitted to JT

    A Continuum-Atomistic Analysis of Transgranular Crack Propagation in Aluminum

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    A concurrent multiscale modeling methodology that embeds a molecular dynamics (MD) region within a finite element (FEM) domain is used to study plastic processes at a crack tip in a single crystal of aluminum. The case of mode I loading is studied. A transition from deformation twinning to full dislocation emission from the crack tip is found when the crack plane is rotated around the [111] crystallographic axis. When the crack plane normal coincides with the [112] twinning direction, the crack propagates through a twinning mechanism. When the crack plane normal coincides with the [011] slip direction, the crack propagates through the emission of full dislocations. In intermediate orientations, a transition from full dislocation emission to twinning is found to occur with an increase in the stress intensity at the crack tip. This finding confirms the suggestion that the very high strain rates, inherently present in MD simulations, which produce higher stress intensities at the crack tip, over-predict the tendency for deformation twinning compared to experiments. The present study, therefore, aims to develop a more realistic and accurate predictive modeling of fracture processes

    New Developments in the Embedded Statistical Coupling Method: Atomistic/Continuum Crack Propagation

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    A concurrent multiscale modeling methodology that embeds a molecular dynamics (MD) region within a finite element (FEM) domain has been enhanced. The concurrent MD-FEM coupling methodology uses statistical averaging of the deformation of the atomistic MD domain to provide interface displacement boundary conditions to the surrounding continuum FEM region, which, in turn, generates interface reaction forces that are applied as piecewise constant traction boundary conditions to the MD domain. The enhancement is based on the addition of molecular dynamics-based cohesive zone model (CZM) elements near the MD-FEM interface. The CZM elements are a continuum interpretation of the traction-displacement relationships taken from MD simulations using Cohesive Zone Volume Elements (CZVE). The addition of CZM elements to the concurrent MD-FEM analysis provides a consistent set of atomistically-based cohesive properties within the finite element region near the growing crack. Another set of CZVEs are then used to extract revised CZM relationships from the enhanced embedded statistical coupling method (ESCM) simulation of an edge crack under uniaxial loading

    The Development of Directional Decohesion Finite Elements for Multiscale Failure Analysis of Metallic Polycrystals

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    Atomistic simulations of intergranular fracture have indicated that grain-scale crack growth in polycrystalline metals can be direction dependent. At these material length scales, the atomic environment greatly influences the nature of intergranular crack propagation, through either brittle or ductile mechanisms, that are a function of adjacent grain orientation and direction of crack propagation. Methods have been developed to obtain cohesive zone models (CZM) directly from molecular dynamics simulations. These CZMs may be incorporated into decohesion finite element formulations to simulate fracture at larger length scales. A new directional decohesion element is presented that calculates the direction of Mode I opening and incorporates a material criterion for dislocation emission based on the local crystallographic environment to automatically select the CZM that best represents crack growth. The simulation of fracture in 2-D and 3-D aluminum polycrystals is used to illustrate the effect of parameterized CZMs and the effectiveness of directional decohesion finite elements

    Atomistic Cohesive Zone Models for Interface Decohesion in Metals

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    Using a statistical mechanics approach, a cohesive-zone law in the form of a traction-displacement constitutive relationship characterizing the load transfer across the plane of a growing edge crack is extracted from atomistic simulations for use within a continuum finite element model. The methodology for the atomistic derivation of a cohesive-zone law is presented. This procedure can be implemented to build cohesive-zone finite element models for simulating fracture in nanocrystalline or ultrafine grained materials
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