5,835 research outputs found

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

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    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

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    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

    Antioxidant,antimicrobial and toxicological properties of Schinus molle L. essential oils

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    Ethnopharmacological relevance: Schinus molle L. has been used in folk medicine as antibacterial, antiviral, topical antiseptic, antifungal, antioxidant, anti-inflammatory, anti-tumoural as well as antispasmodic and analgesic; however, there are few studies of pharmacological and toxicological properties of S. molle essential oils. Aim of the study: The aim of this study was to evaluate the antioxidant and antimicrobial activities of S. molle leaf and fruit essential oils, correlated with their chemical composition and evaluate their acute toxicity. Materials and methods: The chemical composition of S. molle leaf and fruit essential oils were evaluated by GC-FID and GC-MS. Antioxidant properties were determined using the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free radical and β-carotene/linoleic acid methods. Antimicrobial properties were evaluated by the agar disc diffusion method and minimal inhibitory concentration assay. Toxicity in Artemia salina and acute toxicity with behavioural screening in mice were evaluated. Results: The dominant compounds found in leaf and fruit essential oils (EOs) were monoterpene hydrocarbons, namely -phellandrene, β-phellandrene, β-myrcene, limonene and α-pinene. EOs showed low scavenging antioxidant activity by the DPPH free radical method and a higher activity by the β-carotene/linoleic acid method. Antimicrobial activity of EOs was observed for Gram+, Gram– pathogenic bacteria and food spoilage fungi. EOs showed cytotoxicity for Artemia salina and lower toxicity in Swiss mice. Conclusions: The result showed that EOs of leaves and fruits of S. molle demonstrated antioxidant and antimicrobial properties, suggesting their potential use in food or pharmaceutical industries

    CHEMICAL COMPOSITION, ANTIOXIDANT AND ANTIMICROBIAL PROPERTIES OF THREE ESSENTIAL OILS FROM PORTUGUESE FLORA

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    The present work reports on the evaluation of chemical composition and antioxidant and antimicrobial activities of essential oils of three aromatic herbs, growing wild in the south of Portugal, used in traditional food preparations: Foeniculum vulgare, Mentha spicata and Rosmarinus officinalis. The principal components of essential oils were anethole (41.2%) for F. vulgare, carvone (41.1%) for M. spicata and myrcene (23.7%) for R. officinalis. Essential oils showed antioxidant activity either by DPPH radical scavenging method and system β- carotene/acid linoleic method. Antimicrobial activity of essential oils was observed against pathogenic bacteria and yeasts and food spoilage fungi. F.vulgare essential oil showed bacterial activity against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella enteritidis, Staphylococcus aureus, Aspergillus niger and Fusarium oxysporum with MICs of 0.25-0.75mg/mL. M. spicata oil was active against E.coli, S.aureus, C.albicans, A. niger and F. oxysporum with MICs ranging between 0.25 and 0.75mg/mL. R. officinalis essential oil showed activity against E.coli and C.albicans with MICs of 0.5-1.0mg/mL. Having in account the important antioxidant and antimicrobial properties observed in present work, we consider that these essential oils might be useful on pharmaceutical and food industry as natural antibiotic and food preservativ

    Capital structure speed of adjustment heterogeneity across zero leverage and leveraged European firms

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    This paper investigates whether leveraged and zero-leverage firms pursue or not a debt target level and, if so, how fast they adjust to that target. We also investigate how the influence of firms’ debt policy on capital structure speed of adjustment (SOA) changes with different financial systems, macroeconomic conditions, financial constraints and financial flexibility levels. Using the dynamic panel fractional estimator and a sample of European listed firms for the 1995–2016 period, we find that both zero-leverage and leveraged firms actively adjust to a target debt ratio. We also find that, in general, leveraged firms display a significantly higher SOA than zero-leverage firms (27.6 % vs. 22.1 %), with only two exceptions: there are no significant differences when the analysis is restricted to financially constrained firms; and during the 2008 financial crisis zero-leverage firms adjusted significantly faster (46.8 %) than leveraged firms (25.6 %) and relative to non-crisis years (21.6 %).info:eu-repo/semantics/publishedVersio

    Tsallis holographic dark energy in the Brans-Dicke cosmology

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    Using the Tsallis generalized entropy, holographic hypothesis and also considering the Hubble horizon as the IR cutoff, we build a holographic model for dark energy and study its cosmological consequences in the Brans-Dicke framework. At first, we focus on a non-interacting universe, and thereinafter, we study the results of considering a sign-changeable interaction between the dark sectors of the cosmos. Our investigations show that, compared with the flat case, the power and freedom of the model in describing the cosmic evolution is significantly increased in the presence of the curvature. The stability analysis also indicates that, independent of the universe curvature, both the interacting and non-interacting cases are classically unstable. In fact, both the classical stability criterion and an acceptable behavior for the cosmos quantities, including the deceleration and density parameters as well as the equation of state, are not simultaneously obtainable.Comment: Accepted version, Eur. Phys. J. C (2018
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