Prediction of the longitudinal tensile strength of polymer matrix composites

A micromechanical model was developed for the prediction of the longitudinal tensile strength of polymer matrix composites. The model considers successive fibre breaks within an infinitely wide Li-long representative volume element (RVE), Li being the so-called ineffective length. An elastic-plastic stress transfer model is used to define Li and fibre strength is described by a Weibull distribution. The composite strength is obtained by solving numerically an equation for the maximum RVE stress. A simplified closed-form solution derived proved to be in very good agreement with the base formulation. Although there is still significant uncertainty over model input data, predictions agreed well with experimental strengths of carbon fibre composites

South-South cooperation, policy transfer and best-practice reasoning : the transfer of the Solidarity in Literacy Program from Brazil to Mozambique

Mozambique;Brazil;South South cooperation;development programmes;literacy;policy research

STRUCTURAL CHANGE IN THE BRAZILIAN DEMAND FOR IMPORTS: A regime switching approach

The aim of the present paper is to apply a Markov Switching model to check the characteristics of the Brazilian demand for imports equation based on annual data from 1947 to 2002 and on quarterly data from 1978:I to 2002:II. The results show that this model satisfactorily describes the structural and conjunctural characteristics of Brazilian foreign trade in the last decades. The longterm analysis, based on annual data, allowed for the identification of cyclic periods of trade closure and openness that coincide with the historical events of Brazilian economy. The conjunctural analysis, based on quarterly data, indicates different elasticities for a regime with rise and fall in importsMarkov Switching, Error Correction Mechanism, Demand for Imports, Trade Elasticities, Co-integration.

A new data reduction scheme to obtain the mode II fracture properties of Pinus Pinaster wood

In this work a numerical study of the End Notched Flexure (ENF) specimen was performed in order to obtain the mode II critical strain energy released rate (GIIc) of a Pinus pinaster wood in the RL crack propagation system. The analysis included interface finite elements and a progressive damage model based on indirect use of Fracture Mechanics. The difficulties in monitoring the crack length during an experimental ENF test and the inconvenience of performing separate tests in order to obtain the elastic properties are well known. To avoid these problems, a new data reduction scheme based on the equivalent crack concept was proposed and validated. This new data reduction scheme, the Compliance-Based Beam Method (CBBM), does not require crack measurements during ENF tests and additional tests to obtain elastic properties.FCT - POCTI/EME/45573/200

Finite element analysis of the ECT test on mode III interlaminar fracture of carbon-epoxy composite laminates

In this work a parametric study of the Edge Crack Torsion (ECT) specimen was performed in order to maximize the mode III component (GIII) of the strain energy release rate for carbon-epoxy laminates. A three-dimensional finite element analysis of the ECT test was conducted considering a [90/0/(+45/-45)2/(-45/+45)2/0/90]S lay-up. The main objective was to define an adequate geometry to obtain an almost pure mode III at crack front. The geometrical parameters studied were specimen dimensions, distance between pins and size of the initial crack. The numerical results demonstrated that the ratio between the specimen length and the initial crack length had a significant effect on the strain energy release rate distributions. In almost all of the tested configurations, a mode II component occurred near the edges but it did not interfere significantly with the dominant mode III state.FCT - POCTI/EME/45573/200

On the minimal ranks of matrix pencils and the existence of a best approximate block-term tensor decomposition

Under the action of the general linear group with tensor structure, the ranks of matrices $A$ and $B$ forming an $m \times n$ pencil $A + \lambda B$ can change, but in a restricted manner. Specifically, with every pencil one can associate a pair of minimal ranks, which is unique up to a permutation. This notion can be defined for matrix pencils and, more generally, also for matrix polynomials of arbitrary degree. In this paper, we provide a formal definition of the minimal ranks, discuss its properties and the natural hierarchy it induces in a pencil space. Then, we show how the minimal ranks of a pencil can be determined from its Kronecker canonical form. For illustration, we classify the orbits according to their minimal ranks (under the action of the general linear group) in the case of real pencils with $m, n \le 4$. Subsequently, we show that real regular $2k \times 2k$ pencils having only complex-valued eigenvalues, which form an open positive-volume set, do not admit a best approximation (in the norm topology) on the set of real pencils whose minimal ranks are bounded by $2k-1$. Our results can be interpreted from a tensor viewpoint, where the minimal ranks of a degree-$(d-1)$ matrix polynomial characterize the minimal ranks of matrices constituting a block-term decomposition of an $m \times n \times d$ tensor into a sum of matrix-vector tensor products.Comment: This work was supported by the European Research Council under the European Programme FP7/2007-2013, Grant AdG-2013-320594 "DECODA.

South-South Cooperation in Times of Global Economic Crisis

For South-South cooperation, the current moment of global economic downturn is one of anxiety. South-South cooperation was born with the Non-Aligned Movement. It went through a latent period, but re-emerged in the 1990s and early 2000s. The momentum gathered when a handful of middle-income countries such as Brazil, India, Mexico and South Africa were set to improve their position as global players. They had developed some relatively successful social programmes, which they sought to share with other developing countries. Considering that conventional North-South cooperation had turned out to be of limited effectiveness, South-South cooperation gained further impetus.South-South Cooperation in Times of Global Economic Crisis

Business Survival in Portuguese Regions

This work addresses the post-entry performance of employer enterprises for seven regions in Portugal, at the NUT II level, by investigating the structural characteristics of survival, using non-parametric and semi-parametric methods, during the period 1985 to 2007. The last decades of the 20th century were characterized by a period of creative destruction in Portugal. In particular, regions such as Norte, Algarve and Madeira show the highest growth rates in enterprise births, deaths and firm churn. After 2000, firms´ births and deaths get relatively less turbulent. In the non-parametric analysis, we identify statistically significant disparities among regions. Norte has the lowest survival rate and Centro holds the longest surviving firms and the survival gap between the former two regions gets amplified over time. Concerning the semi-parametric analysis, firm’s current size dimension is a strong determinant for the probability of survival, particularly in the Norte and Açores. In industries characterized by high entry rates at the moment of a firm’s birth, post-entry survival becomes harder, especially in the south and in the Portuguese archipelagos, the regions with the lowest number of active employer enterprises. A higher entry rate combined with fast growth rates for any given industry also generates a shorter duration of firms. Manufacturing is the sector where more firms are more likely to abandon the market, particularly in Madeira and Norte. But it is turbulence, given by the sum of firms´ entry and exit rates that exhibits the most significant effect on survival. For every region, except for the Açores, where there is no statistical significance, those that have the highest record of firm turbulence, also display the lowest business survival probabilities. Turbulence decreases severely the survival probabilities of firms located in Madeira and Norte and to a lesser extent in the Algarve.Duration Analysis, Firm dynamics, Entrepreneurship, Regional Analysis.