102 research outputs found

    Predictive roles of organizational and personal factors in work engagement among nurses

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    Objective: To determine the work engagement levels of hospital nurses and the predictive roles that nurses’ personal and organizational characteristics play

    Durability of adhesively bonded joints between pultruded GFRP adherends under hygrothermal and natural ageing

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    This paper presents an experimental and numerical study about the durability of adhesively bonded joints between pultruded glass fibre reinforced polymer (GFRP) adherends for civil engineering applications. Single lap joint (SLJ) specimens were manufactured using either epoxy (EP) or polyurethane (PUR) adhesives and exposed to the following hygrothermal and outdoor ageing conditions for up to 730 days: water and salt water immersion at 20 degrees C and 40 degrees C, continuous condensation at 40 degrees C, salt fog spray at 35 degrees C, and outdoor ageing in Lisbon, Portugal. At predetermined times, the mechanical behaviour of the SLJs was assessed through shear tests, after drying the specimens to constant mass. Results obtained show that hygrothermal ageing detrimentally affected the failure load and stiffness of the SLJs made with both adhesives, although this degradation was balanced to some extent by post-curing effects and the desorption period (recovery after drying). The magnitude of such degradation was not significantly influenced by the immersion media, but was largely affected by temperature. Outdoor ageing did not cause significant changes in terms of stiffness; for both adhesives, failure load presented a moderate increasing trend, with cyclic pattern, reflecting the effects of seasonal changes in weather. For both adhesives, failure always initiated in one of the GFRP adherends, regardless of the ageing process. However, ageing seemed to affect the portion of bond area with either (light) fibre-tear or adhesive failure: in EP-GFRP specimens, the area with adhesive failure (initially null) increased due to ageing, while in PUR-GFRP specimens (significant in unaged joints) it decreased. The final part of the paper presents linear finite element (FE) models of the SLJs exposed to the harsher ageing environment; these models were developed to numerically simulate the mechanical performance of the joints and to assess the evolution of the internal stresses developed in the SLJs due to the effects of hygrothermal ageing in the constituent materials

    The effects of elevated temperature on the bond behaviour of sand coated GFRP bars to concrete – Definition of bond vs. slip relations

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    The use of glass fibre reinforced polymer (GFRP) bars as internal reinforcement of concrete structures has been growing, mainly due to the advantages they present over steel reinforcement, namely their low weight, high strength and corrosion resistance. However, at moderately elevated temperatures, especially when approaching the glass transition temperature (Tg) of the polymeric matrix (usually between 65 and 150 °C), the stiffness, strength and bond properties of these rebars are known to be significantly degraded. The first part of this paper presents an experimental investigation comprising tensile and pull-out tests on sand coated GFRP rebars at elevated temperatures under steady-state conditions; the tensile tests were carried out up to 300 °C, whereas the pull-out tests were performed up to 140 °C (measured at the GFRP-concrete interface); two embedment lengths of the rebars were considered. The obtained results confirmed that the stiffness and strength of the GFRP-concrete interface are significantly reduced with temperature increase, especially when the Tg of the GFRP rebars is approached and exceeded. In the second part of the paper, analytical bond vs. slip relations for the GFRP-concrete interface are proposed for each of the tested temperatures; the defining parameters of these local laws were calibrated with the experimental data from the pull-out tests. Moreover, the accuracy of two empirical (relaxation) models in predicting the GFRP-concrete bond strength reduction with temperature was also assessedFCT (project PTDC/ECM-EST/1882/2014) and CERIS for funding the research, Secil and Unibetão for supplying the concrete and Owens Corning for supplying the GFRP rebars. The first and second authors also wish to thank the financial support of FCT through scholarships SFRH/BD/129681/2017 and SFRH/BDP/108319/201

    Efeito da temperatura elevada na aderĂȘncia entre betĂŁo e varĂ”es de GFRP com acabamento em areia – Ensaios de arrancamento e determinação de leis bond-slip

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    O uso de varĂ”es de polĂ­mero reforçado com fibra de vidro (GFRP) como armaduras de estruturas (novas ou requerendo reforço estrutural) de betĂŁo armado tem vindo a crescer, dadas as vĂĄrias vantagens que estes varĂ”es apresentam comparativamente aos varĂ”es de aço, nomeadamente o baixo peso prĂłprio e sua nĂŁo suscetibilidade Ă  corrosĂŁo. Contudo, a temperaturas moderadamente elevadas, especialmente na proximidade da temperatura de transição vĂ­trea (Tg) da matriz polimĂ©rica (geralmente entre 65-150 ÂșC), a resistĂȘncia, a rigidez e as propriedades de aderĂȘncia destes varĂ”es podem ser nefastamente afetadas. A primeira parte deste artigo apresenta um estudo experimental focado na aderĂȘncia entre betĂŁo e varĂ”es com acabamento de areia expostos a temperaturas moderadamente elevadas. Ensaios de arrancamento foram realizados em varĂ”es de GFRP embebidos em cilindros de betĂŁo a 20 ÂșC, 40 ÂșC, 60 ÂșC, 80 ÂșC, 100 ÂșC e 140 ÂșC. Dois comprimentos aderentes foram considerados, correspondendo a 5 e 9 vezes o seu diĂąmetro. Os provetes foram primeiramente aquecidos atĂ© uma temperatura objectivo (medida na interface betĂŁo-GFRP) e depois traccionados atĂ© Ă  rotura. A carga aplicada e o deslizamento dos varĂ”es nas extremidades livre e carregada foram medidos durante o ensaio. Os resultados obtidos confirmaram que a rigidez e a resistĂȘncia na interface betĂŁo-GFRP sĂŁo significativamente reduzidas com a temperatura, especialmente na proximidade e apĂłs a Tg dos varĂ”es. Na segunda parte do artigo, relaçÔes bond-slip para a interface betĂŁo-GFRP sĂŁo propostas para cada uma das temperaturas testadas. Estas relaçÔes foram obtidas atravĂ©s de uma metodologia numĂ©rica na qual os dados experimentais provenientes dos ensaios de arrancamento foram utilizados para calibrar os parĂąmetros dasleis bond-slip locais.Fundação para a CiĂȘncia e Tecnologia – FCT (projecto PTDC/ECM-EST/1882/2014) e aos CERIS pelo financiamento desta investigação, Ă  Secil/UnibetĂŁo pelo fornecimento de betĂŁo e Ă  Hughes Brothers pelo fornecimento dos varĂ”es de GFRP. O primeiro e segundo autores tambĂ©m gostariam de agradecer o financiamento da FCT atravĂ©s das bolsas SFRH/BD/129681/2017 e SFRH/BDP/108319/201

    Quasiparticle interference and strong electron-mode coupling in the quasi-one-dimensional bands of Sr2RuO4

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    The single-layered ruthenate Sr2_2RuO4_4 has attracted a great deal of interest as a spin-triplet superconductor with an order parameter that may potentially break time reversal invariance and host half-quantized vortices with Majorana zero modes. While the actual nature of the superconducting state is still a matter of controversy, it has long been believed that it condenses from a metallic state that is well described by a conventional Fermi liquid. In this work we use a combination of Fourier transform scanning tunneling spectroscopy (FT-STS) and momentum resolved electron energy loss spectroscopy (M-EELS) to probe interaction effects in the normal state of Sr2_2RuO4_4. Our high-resolution FT-STS data show signatures of the \beta-band with a distinctly quasi-one-dimensional (1D) character. The band dispersion reveals surprisingly strong interaction effects that dramatically renormalize the Fermi velocity, suggesting that the normal state of Sr2_2RuO4_4 is that of a 'correlated metal' where correlations are strengthened by the quasi 1D nature of the bands. In addition, kinks at energies of approximately 10meV, 38meV and 70meV are observed. By comparing STM and M-EELS data we show that the two higher energy features arise from coupling with collective modes. The strong correlation effects and the kinks in the quasi 1D bands may provide important information for understanding the superconducting state. This work opens up a unique approach to revealing the superconducting order parameter in this compound