Repositório Institucional da Universidade de Aveiro
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Development of an oil spill hazard scenarios database for risk assessment
No full textThe occurrence of oil spills in coastal regions may have catastrophic consequences on the environment and severe socio-economic impacts. This work presents a new methodology to evaluate the risk associated with oil spills in coastal zones and estuaries, and illustrates its application in a coastal lagoon (Ria de Aveiro, Portugal). A ranked list of the hydrodynamic scenarios under which oil spills are most likely generated through the analysis of 33 years of wave and wind data, retrieved from the ERA-INTERIM project database, and from the analysis of oil spills that occurred in the Atlantic Iberian shelf. Considering six spill locations and a single oil type spill inside the Aveiro harbor, the database resulted in approximately 3500 simulations. Hydrodynamic simulations were made with the MORSYS2D modeling system, a soft coupling of the hydrodynamic model ELCIRC and the wave model SWAN. The high-accuracy, unstructured grid, oil fate model VOILS was used in 2D mode to simulate the transport and the oil weathering processes at the surface and in the intertidal areas. The hazard assessment analysis included the determination of the trajectory of the plumes, the shoreline retention areas affected by the oil and their oil exposure time. Time evolution of the oil properties, such as the oil evaporation rate and emulsification processes of the mixture, are provided to support clean-up operations, as well as robustness controls such as oil mass balance
HARD: Hybrid Adaptive Resource Discovery for Jungle Computing
No full textIn recent years, Jungle Computing has emerged as a distributed computing paradigm based on simultaneous combination of various hierarchical and distributed computing environments which are composed by large number of heterogeneous resources. In such a computing environment, the resources and the underlying computation and communication infrastructures are highly-hierarchical and heterogeneous. This creates a lot of difficulty and complexity for finding the proper resources in a precise way in order to run a particular job on the system efficiently. This paper proposes Hybrid Adaptive Resource Discovery (HARD), a novel efficient and highly scalable resource-discovery approach which is built upon a virtual hierarchical overlay based on self organization and self-adaptation of processing resources in the system, where the computing resources are organized into distributed hierarchies according to a proposed hierarchical multi-layered resource description model. The proposed approach supports distributed query processing within and across hierarchical layers by deploying various distributed resource discovery services and functionalities in the system which are implemented using different adapted algorithms and mechanisms in each level of hierarchy. The proposed approach addresses the requirements for resource discovery in Jungle Computing environments such as high hierarchy, high-heterogeneity, high-scalability and dynamicity. Simulation results show significant scalability and efficiency of the proposed approach over highly heterogeneous, hierarchical and dynamic computing environments
Magnetoelectric coupling effect in transition metal modified polycrystalline BiFeO3 thin films
No full textRare-earth (Sm) and transition metal (Co) modified polycrystalline BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2/Si substrate successfully through pulsed laser deposition (PLD) technique. Piezoelectric, leakage current and temperature dependent dielectric and magnetic behaviour were investigated for the films. Typical \"butterfly-shaped\" loop were observed in BSFCO films with an effective piezoelectric constant (d(33)) similar to 94 pm/V at 0.6 MV/cm. High dielectric constant similar to 900 and low dielectric loss similar to 0.25 were observed at room temperature. M-H loops have shown relatively high saturation magnetization similar to 35 emu/cm(3) at a maximum field of H similar to 20 kOe. Enhanced magnetoelectric coupling response is observed under applied magnetic field. The multiferroic, piezoelectric, leakage current behaviours were explored. Such studies should be helpful in designing multiferroic materials based on BSFCO films. (C) 2014 Elsevier B.V. All rights reserved
Rigid polyurethane foams derived from cork liquefied at atmospheric pressure
No full textThe aim of this study was to evaluate the possibility of using polyols derived from liquefied cork in the production of novel bio-based polyurethane foams (PUFs). For that purpose, different liquefaction conditions were used at atmospheric pressure and moderate temperature where poly(ethylene glycol) and glycerol were used as solvents and sulfuric acid as catalyst. The ensuing polyols were used to produce foams which were characterized using structural, morphological, thermal and mechanical analyses to demonstrate that liquefaction conditions play a crucial role in the properties of the foams. The resulting foams exhibited the typical cellular structure of PUFs with low densities (57.4-70.7 kgm(-3)) and low thermal conductivities (0.038-0.040 Wm(-1)K(-1)). However, the mechanical properties differed significantly depending on the liquefaction conditions. The best stress-strain results were obtained for PUFs prepared using the polyol with lowest I-OH and water content (Young's modulus of 475.0 kPa, compressive stress (sigma(10%)) of 34.6 kPa and toughness of 7397.1 Jm(-3)). This PUF was thermally stable up to 200 degrees C and presented a glass transition temperature of around 27 degrees C. The results obtained demonstrate that these polyols from liquefied cork yield PUFs that are adequate materials for insulation applications. (c) 2014 Society of Chemical Industr
Post-synthetic modification of crystal-like periodic mesoporous phenylene-silica with ferrocenyl groups
No full textAmination of crystal-like 1,4-phenylene-bridged periodic mesoporous organosilica (Ph-PMO) was achieved with about 35% conversion of phenylene groups. Ferrocenylimine groups were subsequently anchored onto this material by condensation of acetylferrocene with amino groups. Elemental analysis indicated that about 15% of amino groups in PMO-NH2 were derivatized, resulting in an iron loading of 0.21 mmol g(-1). Evidence for the presence of ferrocenylimine groups in the derivatized material (PMO-Fc) was obtained from C-13 cross-polarization (CP) magic-angle spinning (MAS) NMR and FT-IR spectroscopies. PMO-Fc was further characterized by Si-29 MAS NMR spectroscopy, powder X-ray diffraction (XRD), N-2 adsorption-desorption, and thermogravimetric analysis (TGA). Powder XRD and N-2 adsorption-desorption data for PMO-NH2 and PMO-Fc indicated that the mesoporous structure and molecular-scale periodicity in PMO-NH2 were largely retained upon treatment with acetylferrocene. The material PMO-Fc was examined as a catalyst for the oxidation of styrene at 55 degrees C using hydroperoxides as oxidants. The reaction products were benzaldehyde (major) and styrene oxide (minor), with the aldehyde being formed in yields of 25-27% at 24 h. Recycling experiments indicated that the material was susceptible to leaching of catalytically active species into the liquid phase due to the pronounced water sensitivity of the azomethine linkage. (C) 2013 Elsevier B.V. All rights reserved
Low-temperature dielectric relaxations in Y-doped strontium titanate ceramics
No full textThe structural and low-frequency dielectric properties of Y-doped strontium titanate ceramics prepared by the conventional mixed oxide method are investigated. The lattice parameter is found to decrease linearly in the Sr1-1.5xYxTiO3 system, confirming the incorporation of Y onto the Sr site of perovskite lattice of strontium titanate up to the solid solubility limit below x = 0.05. The real and imaginary parts of the dielectric permittivity of Sr1-1.5xYxTiO3 ceramics exhibit a relaxation between 100 Hz and 1 MHz in the temperature range 10-40 K, slightly shifting to higher temperatures with increasing Y content. Such dielectric behavior, yielding real part of the dielectric permittivity up to 35 000, is attributed to the relaxation of individual dipoles formed by off-center displacement of Y3+ ions on Sr sites in a highly polarizable lattice of strontium titanate. The other dielectric relaxation observed in Sr1-1.5xYxTiO3 from 125 to 300 K is attributed to the oxygen vacancy related mechanisms
Extrusion of ceramic emulsions: Plastic behavior
No full textThis paper presents the plastic characterization of several extruded ceramic emulsions prepared by emulsification of different ceramic suspensions: i) red clay, ii) kaolin and iii) alumina, which were performed in order to obtain some insights to upscale the ceramic emulsion extrusion process. Stress-deformation curves obtained by compression of the pre-extruded bodies were used to obtain the plasticity characterization of the emulsions with different water contents. Deformation amplitude, yield stress and rupture stress revealed the most sensitive parameters, thus giving valuable information about the plastic behavior of the ceramic emulsions, as well as important guidelines for extrusion upscale. The microstructural features of the sintered bodies were kept constants even after the extrusion process, making this process be feasible for large-scale production of cellular ceramic bodies. (C) 2014 Elsevier B.V. All rights reserved
Influence of TiO2 host crystallinity on Er3+ light emission
No full textThis work presents a study of the luminescence properties of Er3+ when included into two different TiO2 hosts: a polycrystalline and an amorphous host. The two host environments were produced by depositing two thin films with different Er3+ concentration using radio-frequency magnetron sputtering. Structural analysis revealed the presence of the rutile and anatase phases in the polycrystalline film. Time-resolved and steady-state photoluminescence measurements evidenced the presence of two distinct local Er3+ environments in the polycrystalline host. For the amorphous TiO2 host, only one Er3+ environment was observed, which differed from the two environments in the polycrystalline host. A method for extracting a fast and slow time-resolved emission spectrum from the two observed local environments in the polycrystalline host is also presented. (C) 2016 Optical Society of Americ
In vitro Bioactivity of Polycaprolactone/Bioglass Composites
No full textA series of Polycaprolactone and Bioglass in the 85SiO 2-10CaO-5P2O 5 (mol. %) systems were synthesized at different quantity of the organic/inorganic co mponents. The 85S Bioglass was prepared via sol-gel method. It was added to the Polycaprolactone matrix at 20, 50 and 80 weight (wt.) %, respectively. In vitro bioactivity of the prepared composites was evaluated in 1.5 Simu lated Body Flu id (1.5 SBF). The obtained composite materials before and after static in vitro test were characterized by FTIR and SEM. The obtained experimental data proved that the synthesized co mposites exhibit good in vitro bioactivity. After immersion in 1.5SBF, SEM depicts the presence of nano-needle-like hydro xyapatite on the immersed 20PCL/80BG and 50PCL/50BG samples
Influence of fired clay brick waste additions on the durability of mortars
No full textThe use of metakaolin is known to help improve properties of Portland cement-based mortars. The presumed similarities between the characteristics of metakaolin and those of a powdered (<45 mu m) fired clay brick clean waste (CBW) led to the investigation of the effect on the durability of mortars of partial replacement (10, 25 and 40 wt.%) of Portland cement by CBW. Properties such as 28 and 90 days-compressive strength, water absorption, apparent porosity, absorption by capillarity, chloride retention, carbonation depth and sulphate resistance were evaluated. The CBW-containing cured mortars showed improved strength and density, as the result of combined physical and pozzolanic pore filling effect of added CBW. However, CBW-free mortar exhibited larger spreading and, being more porous, higher sulphate resistance and ability to absorb chlorides. Optimum performance was found for the 40 wt.% CBW mortar whose compressive strength can be up to 130% higher than that of the CBW-free mortar. (C) 2015 Elsevier Ltd. All rights reserved