ES - Artigos em revistas internacionais
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- Dye-sensitized 1D anatase TiO2 nanorods for tunable efficient photodetection in the visible rangePublication . Parreira, P.; Torres, Erica; Nunes, Clarisse; Carvalho, C. Nunes de; Lavareda, G.; Amaral, A.; Brites, Maria JoãoTiO2 films with enhanced photosensitivity were deposited on alkali free glass substrates without intentional substrate heating by pulsed DC magnetron reactive sputtering with an average thickness of about 2 μm. Three dyes, commercial N719 and two new organic dyes were impregnated in order to control the optical spectral selectivity of such films. The type of dye used proved to dramatically influence the device's response to radiation pulses. The practical breakthrough is the use of different dyes according to the region of the electromagnetic spectrum one wants to detect. Devices with photocurrent 6 orders of magnitude higher than the dark current (from ∼2 × 10−12 to 2 × 10−6 A for a 100 V bias) were fabricated with a spectral response within the visible range of the electromagnetic spectrum. In addition, this approach is likely to allow for the fabrication of hybrid photodetectors on cheap heat sensible flexible polymeric substrates.
- Impact of different internal convection control strategies in a non-evacuated CPC collector performancePublication . Horta, Pedro; Henriques, J.C.C.; Collares-Pereira, M.Over the last decade the technological advances observed in solar collector materials, namely better spectrally selective absorber coatings and ultra clear glass covers, contribute to performance improvements and translate into higher operational temperature ranges with higher efficiency values. While the use of Evacuated Tube Collectors (ETCs) is becoming widespread in the thermal conversion of solar energy, non-evacuated solar collectors still hold advantages at manufacturing, reliability and/or cost levels, making them interesting and competitive for a large range of applications, in particularly, in temperature ranges up to 80 °C. However, these advantages have not prevented the major drawback of these collectors when compared to ETCs: thermal losses due to internal convection which prevent their general use in the range of operating temperatures up to 150 °C.Insulation, double glazing or selective coatings can be used in non-evacuated collectors to reduce heat losses. To prevent internal convection losses in these solar collectors, different control strategies have been studied, such as the adoption of different inert gases within the collector cavity, physical barriers reducing air flow velocities over the absorber or cover surfaces or the use of concentration. In the present article, an assessment of adopting such internal convection control strategies in a CPC collector is presented. Each of the presented strategies is assessed in terms of the resulting collector optical and thermal characterization parameters and yearly collector yield. For this purpose, an integrated tool allowing the design, optical and thermal characterization of CPC collectors was developed. The results obtained provide valuable guidelines for anyone wishing to implement any of these strategies in a new collector design.
- Chemical Activities, a(H) and a(X), of Constituents in H2X Type Gas Molecules (X = O or S) at Arbitrary Degree of DissociationPublication . Shohoji, NobumitsuChemical activities, a(X) and a(H), of constituents, X and H, in H2X type gas molecules (X = S or O) were evaluated as functions of temperature T and extent α of dissociation adapting a thermodynamic analysis procedure developed by Katsura for interpreting enhanced a(N) and a(H) in NH3 gas molecules with suppressed α by flowing. Present analysis results showed that both H2S and H2O gas molecules are chemically rather inert even at comparatively low α unlike nitrogen-family tri-hydrides XH3 that were proved to yield high chemical activity of each constituent in a state being away from thermodynamic equilibrium. The parameter α referring to the extent of dissociation of HnX type gas molecules appears to be a significant parameter in evaluating the chemical activities, a(X) and a(H), in the HnX gas molecules that are remained non-dissociated.
- Statistical Thermodynamic Analysis for Isothermal Hydrogenation Performances of Mg2-yPryNi4Intermetallics (y = 0.6, 0.8, 1.0)Publication . Shohoji, NobumitsuIsothermal hydrogenation performances of intermetallic Mg2-yPryNi4 alloys with y = 0.6, 0.8 and 1.0 reported by Terashita et al.were analyzed on the basis of statistical thermodynamics under a simplifyinga priori assumption of constant nearest neighbourH-H interactionE(H-H) in a given phase at arbitrary T aiming at characterizing basic aspects of state of H atoms in the interstitial sites in H-storage alloy. To fulfill this a priori assumption, number θ of available interstitial sites per metal atom was chosen by preliminary search attempt at the onset of the statistical thermodynamic analysis. Primary H solution in Mg2-yPryNi4 was analyzed by the model with θ = 0.15. The chosen value 0.15 for the model analysis was close to be 1/6 (≈ 0.167) which was half of 1/3 (=[Mg + Pr]/[Mg + Pr + Ni])implying that about half of the (Mg + Pr)-related interstitial sites were provided as the available sites for occupation by H atoms in the primary H solution of Mg2-yPryNi4. On the other hand, hypo-stoichiometric M4H3 type hydride of Mg2-yPryNi4 was analyzed by the model with θ = 0.75 and θ' = 0.333 where ' refers to the lower limiting composition of the phase. This model yielded situation with E(H-H) = 0 for any Mg2-yPryNi4examined. Chosen value of θ' = 0.333 appeared to imply that the filling of Ni-related interstitial sites by H atoms started after preferential full occupation of the (Mg + Pr)-related interstitial sites by H atoms in the two-phase equilibrium range at invariable p(H2) plateau during H-charging.
- Novel two-step processing route combining mechanical alloying and microwave hybrid sintering to fabricate dense La9.33Si2Ge4O26 for SOFCsPublication . Santos, Mário João dos; Alves, Cátia; Oliveira, Fernando Almeida Costa; Marcelo, Teresa; Mascarenhas, João; Cavaleiro, A.; Trindade, B.In this work, microwave hybrid sintering at 1300 and 1350 °C was carried out for densification of La9.33Si2Ge4O26 mechanically alloyed powder with apatite structure. The pellets sintered at these two temperatures present the same structure (apatite) with relative densities of 92 and 96%, respectively. Mechanical analysis performed on sintered materials revealed the following results: hardness of 7.1 and 8.0 GPa, Young's modulus of 122 and 133 GPa, yield strength of 1807 and 2073 MPa and fracture toughness of 1.5 and 1.0 MPa m1/2, respectively.
- CdTe nano-structures for photovoltaic devicesPublication . Corregidor, V.; Alves, L. C.; Franco, N.; Barreiros, M. Alexandra; Sochinskii, N. V.; Alves, E.CdTe nano-structures with diameter of ∼100 nm and variable length (200–600 nm) were fabricated on glass substrates covered with conductive buffer layers such as NiCr, ZAO (ZnO:Al2O3 + Ta2O5) or TiPd alloys. The fabrication process consisted of the starting vapour deposition of metal catalyst dropped layer followed by the isothermal catalyst-prompted vapour growth of CdTe nano-structured layer of controllable shape and surface filling. The effect of buffer layers on the crystallographic orientation and thickness of CdTe nano-structured layers is investigated by means of IBA techniques, SEM and X-ray diffraction. It was shown that the formed CdTe nano-layers have a cubic structure, mainly oriented towards the [1 1 1] crystallographic direction, except for those grown on ZAO layer where the X-ray diffraction signal is very weak to be associated to any crystallographic form. The RBS spectra recorded on different areas of each sample type showed an almost constant thickness and SEM images revealed an homogeneous and dense distribution of the structures. It was also possible to study the first stage of the nano-structures grown on the Bi2Te3 seeds.
- Biomarkers of exposure to metal dust in exhaled breath condensate: methodology optimizationPublication . Félix, P. M.; Franco, C.; Barreiros, M. Alexandra; Batista, B.; Bernardes, S.; Garcia, S. M.; Almeida, A. B.; Almeida, S. M.; Wolterbeek, H. Th.; Pinheiro, TeresaIn occupational assessments where workers are exposed to metal dust, the liquid condensate of exhaled breath (EBC) may provide unique indication of pulmonary exposure. The main goal of this study was to demonstrate the quality of EBC to biological monitoring of human exposure. A pilot study was performed in a group of metal dust–exposed workers and a group of nonexposed individuals working in offices. Only metal dust–exposed workers were followed along the working week to determine the best time of collection. Metal analyses were performed with inductively coupled plasma mass spectrometry (ICP-MS). Analytical methodology was tested using an EBC sample pool for several occupationally exposed metals: potassium, chromium, manganese, copper, zinc, strontium, cadmium, antimony, and lead. Metal contents in EBC of exposed workers were higher than controls at the beginning of the shift and remained augmented throughout the working week. The results obtained support the establishment of EBC as an indicator of pulmonary exposure to metals.
- The earrings of Pancas treasure: Analytical study by X-ray based techniques – A first approachPublication . Tissot, Isabel; Tissot, M.; Manso, M.; Alves, L. C.; Barreiros, M. Alexandra; Marcelo, Teresa; Carvalho, M. L.; Corregidor, V.; Guerra, M. F.The development of new metallurgical technologies in the Iberian Peninsula during the Iron Age is well represented by the 10 gold earrings from the treasure of Pancas. This work presents a first approach to the analytical study of these earrings and contributes to the construction of a typological evolution of the Iberian earrings. The manufacture techniques and the alloys composition were studied with three complementary X-ray spectroscopy techniques: portable EDXRF, μ-PIXE and SEM–EDS. The results were compared with earrings from the same and previous periods.
- Effect of the sintering conditions on the morphology of La9.33Si2Ge4O26 oxyapatite for SOFCs electrolytesPublication . Macatrão, Mafalda; Santos, Mário João dos; Alves, Cátia; Oliveira, Fernando Almeida Costa; Marcelo, Teresa; Mascarenhas, João; Trindade, B.Solid oxide fuel cells (SOFCs) are devices that allow direct conversion of chemical to electrical energy through an electrochemical reaction in a cleaner and more efficient way than conventional processes (eg. gas turbines). They are characterized by the use of a solid oxide material as the electrolyte. Yttria-stabilised zirconia (YSZ) has traditionally been used in SOFCs electrolytes at temperatures in the range of 850-1000 °C. Recent research is being focused on the development of new materials with increased ionic conductivity at intermediate temperatures (500-800ºC) as alternative materials to YSZ. Rare earth silicates with an apatite-type structure, such as doped lanthanum oxides of general formula La10(MO4)6O2, where M = Ge, Co, Si, Al, or P, are among these materials. The major limitation associated with the manufacture of these materials is their poor sinterability, which requires high sintering temperatures (1600ºC).
- Exhaled breath condensate as a biomonitor for metal exposure: a new analytical challengePublication . Barreiros, M. Alexandra; Pinheiro, Teresa; Félix, P. M.; Franco, C.; Santos, Mário João dos; Araújo, F.; Freitas, Maria do Carmo; Almeida, S. M.The study of exhaled breath condensate (EBC) obtained by cooling exhaled air under conditions of spontaneous breathing is considered one of the areas with higher interest in respiratory health research. The use of EBC for elemental determination in occupational exposure requires a standard methodological procedure to implement its practice in occupational studies. EBC is an inhomogeneous sample with organic and particulate matter in suspension, which may hamper analytical results reliability. Total reflection X-ray fluorescence and inductive coupled-plasma mass spectrometry (ICP-MS) techniques were chosen as both are multielemental, require small sample volumes and have appropriate detection limits. Estimation of the overall uncertainty in both techniques was carried out using a pool of EBC collected from a group of workers of a lead processing industry to perform precision and trueness studies for K, Mn, Cu, Cd, Sb and Pb. Precision was estimated in terms of repeatability using the native EBC sample pool and trueness in terms of recovery obtained from spiking aliquots of the EBC pool with K, Mn, Cu, Cd, Sb and Pb at different concentrations. Recovery was the most significant contribution to total uncertainty. The overall uncertainties obtained for ICP-MS enabled to discriminate between groups of individuals exposed to different levels of contaminants. Therefore EBC proved to be useful in human biomonitoring.