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

Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates

In this study we investigate magnetic properties, surface morphology and crystal structure in iron nanoclusters electrodeposited on lightly-doped (100) n-type silicon substrates. Our goal is to investigate the spin injection and detection in the Fe/Si lateral structures. The samples obtained under electric percolation were characterized by magnetoresistive and magnetic resonance measurements with cycling the sweeping applied field in order to understand the spin dynamics in the as-produced samples. The observed hysteresis in the magnetic resonance spectra, plus the presence of a broad peak in the non-saturated regime confirming the low field microwave absorption (LFMA), were correlated to the peaks and slopes found in the magnetoresistance curves. The results suggest long range spin injection and detection in low resistive silicon and the magnetic resonance technique is herein introduced as a promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure

A new methodology for the characterization of mode II fracture of pinus pinaster wood

In this study, the End Notched Flexure (ENF) fracture test was used to obtain the mode II Rcurve of the Pinus pinaster wood in the RL crack propagation system. The test method was numerically and experimentally analyzed. In the numerical study, three (3D) and twodimensional (2D) finite element analyses were conducted to determine the mode II critical strain energy release rate (GIIc) and the respective R-curve. Firstly, the 3D analysis was performed in order to obtain the strain energy release rates distributions at the crack tip, and consequently, to identify the presence of spurious fracture modes that could affect the measured GIIc. The P-δ-a values determined from the 3D model were compared with the same values obtained from the 2D model. The main objective was to validate the 2D model, which is computationally less expensive. On the other hand, measurement of the crack length in the ENF test is quite difficult in wood because crack tends to close during propagation. To avoid this experimental problem a Compliance-Based Beam Method (CBBM), based on equivalent crack approach, is proposed. Moreover, this method does not require additional experimental tests to obtain the elastic properties. Experimental tests were also executed in order to verify the numerical results. The aim is to introduce the CBBM as a standard data reduction scheme in order to measure the GIIc value

Como Funciona o Xénon: Mecanismos de Neuro e Cardioprotecção

INTRODUCTION: The Xenon, a noble gas, has anesthetics properties, associated with remarkable hemodynamic stability as well as cardioprotective, neuroprotective proprieties. Its physicochemical characteristics give him a quick induction and emergence of anesthesia, being free of deleterious effects in all organs and showing no teratogenicity. Such properties have led to a growing interest in improving the knowledge about this noble gas, in order to assess the mechanisms of neuro and cardioprotection induced and to assess the clinical indications for its use. MATERIAL AND METHODS: Qualitative review of clinical trials on anesthesia with xenon. Studies were identified from MEDLINE and by hand-searching, using the following keywords: xenon, xenon anestesia, xenon neuroprotection, xenon cradioprotection. RESULTS: After several studies, including two randomized multicenter controlled trials, the use of xenon as an anesthetic in patients ASA I-II was approved in March 2007. However his use in clinical practice has been strongly limited by it's high price. It seems unlikely that the advantages it offers in relation to other anesthetics justify it's use in patients ASA I-II. Although, xenon may be a valuable asset in the reduction of co-morbilities and mortality in anesthesia of patients ASA III-IV, unfortunately, there are no large randomized control studies to prove it. DISCUSSION: Unfortunately, there are still no randomized or multicentric studies showing a favourable cost-benefit profile of xenon in ASA III-IV patients vs. other anaesthetics. CONCLUSION: The usefulness of xenon in Anesthesiology requires more studies to be defined

Finite-momentum condensate of magnetic excitons in a bilayer quantum Hall system

We study the bilayer quantum Hall system at total filling factor \nu_T = 1 within a bosonization formalism which allows us to approximately treat the magnetic exciton as a boson. We show that in the region where the distance between the two layers is comparable to the magnetic length, the ground state of the system can be seen as a finite-momentum condensate of magnetic excitons provided that the excitation spectrum is gapped. We analyze the stability of such a phase within the Bogoliubov approximation firstly assuming that only one momentum Q0 is macroscopically occupied and later we consider the same situation for two modes \pm Q0. We find strong evidences that a first-order quantum phase transition at small interlayer separation takes place from a zero-momentum condensate phase, which corresponds to Halperin 111 state, to a finite-momentum condensate of magnetic excitons.Comment: 18 pages, 11 figures, final versio

Calibration of parameters in Dynamic Energy Budget models using Direct-Search methods

Dynamic Energy Budget (DEB) theory aims to capture the quantitative aspects of metabolism at the individual level, for all species. The parametrization of a DEB model is based on information obtained through the observation of natural populations and experimental research. Currently the DEB toolbox estimates these parameters using the Nelder–Mead Simplex method, a derivative-free direct-search method. However, this procedure presents some limitations regarding convergence and how to address constraints. Framed in the calibration of parameters in DEB theory, this work presents a numerical comparison between the Nelder–Mead Simplex method and the SID-PSM algorithm, a Directional Direct-Search method for which convergence can be established both for unconstrained and constrained problems. A hybrid version of the two methods, named as Simplex Directional Direct-Search, provides a robust and efficient algorithm, able to solve the constrained optimization problems resulting from the parametrization of the biological models.authorsversionpublishe

Diatoms of temporary and permanent watercourses in Southern Europe (Portugal)

The potential importance of benthic diatoms in Mediterranean watercourses has received limited academic attention historically. This study sought to provide baseline information for this poorly studied group. Temporary and permanent watercourses in Portugal differ in catchment characteristics, climatic variables and water chemistry. The benthic diatom communities were characterized in terms of ecological preferences and conservation status for taxa with relative abundance above 1% in at least one site covering 39 temporary sites (109 taxa) and 53 permanent sites (130 taxa). The low-profile guild dominated both temporary and permanent watercourses, followed by the high-profile and motile guilds. Indicator value analysis indicated that Amphora copulata, Cocconeis placentula, Diploneis separanda, Encyonopsis subminuta, Fragilaria radians, Gomphonema olivaceum, Gomphonema truncatum, Halamphora veneta, Navicula radiosa, Navicula veneta, Sellaphora seminulum and Ulnaria acus were indicators of temporary watercourses, whereas Encyonema minutum, Eunotia minor, Fragilaria rumpens, Fragilaria cf. socia and Navicula rhynchocephala were characteristic of permanent watercourses. Ecological preferences of indicator taxa were inferred on the basis of environmental variables that differed significantly between temporary and permanent watercourses. The importance of temporary watercourses for the maintenance of diatom biodiversity is discussed and explored