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Santiago do Cacém, Portugal

Tedim J.,University of Porto | Tedim J.,Campus Universitrio Of Santiago | Patricio S.,University of Porto | Fonseca J.,University of Porto | And 4 more authors.
Synthetic Metals | Year: 2011

Electroactive polymer films based on [Ni(salen)]-type complexes were fabricated and their electronic properties characterized using in situ UV-visible spectroelectrochemistry. The extent of π electronic delocalisation and electronic asymmetry were manipulated by introduction of different conjugated imine bridges. Measured electronic spectra were interpreted in terms of polaronic states in the band gap and metal-oxidized ligand charge transfer bands. Density functional theory (DFT) calculations for the monomers showed that the HOMO orbital (which governs oxidation potential) is ligand-dominated, and that substituents with greater electronic delocalisation in the diimine bridge decrease the HOMO-LUMO energy gap. Replacement of methyl by methoxyl substituents in the aldehyde moiety increases the calculated dipole moment. Substitution-driven variations in EHOMO-ELUMO for the monomers were reflected in the corresponding polymer band gaps, demonstrating that monomer electronic properties can be used predictively in the manipulation of polymer electronic properties. An important strategic aspect is the correlation of DFT predictions with the observed electronic properties of monomeric and polymeric materials; the extent to which such modelling can be used to optimise synthetic effort is discussed. © 2011 Elsevier B.V. Source

Rodriguez J.,Campus Universitrio Of Santiago | Monteiro V.,Campus Universitrio Of Santiago | Gomes A.,Portugal Telecom Inovao S.A. | Di Renzo M.,French National Center for Scientific Research | And 9 more authors.
Eurasip Journal on Wireless Communications and Networking | Year: 2010

The Next Generation Network (NGN) vision is tending towards the convergence of internet and mobile services providing the impetus for new market opportunities in combining the appealing services of internet with the roaming capability of mobile networks. However, this convergence does not go far enough, and with the emergence of new coexistence scenarios, there is a clear need to evolve the current architecture to provide cost-effective end-to-end communication. The LOOP project, a EUREKA-CELTIC driven initiative, is one piece in the jigsaw by helping European industry to sustain a leading role in telecommunications and manufacturing of high-value products and machinery by delivering pioneering converged wireless networking solutions that can be successfully demonstrated. This paper provides an overview of the LOOP project and the key achievements that have been tunneled into first prototypes for showcasing next generation services for operators and process manufacturers. Copyright © 2010 J. Rodriguez et al. Source

Vujicic Z.,Campus Universitrio Of Santiago | Pavlovic N.B.,Campus Universitrio Of Santiago | Parca G.,Campus Universitrio Of Santiago | Teixeira A.,Campus Universitrio Of Santiago | Teixeira A.,Nokia Inc.
Physica Scripta | Year: 2012

We investigate the possibilities of controlling and exploiting the spatial evolution of the four-wave mixing (FWM) idler in a fiber optical parametric amplifier, considering standard single-mode fibers. We found that the use of high pump powers, for a given requirement on the signal extinction ratio and frequency separation between pump and signal, can considerably affect the optical signal-to-noise ratio on the idler frequency due to the residual modulation. We observe that by choosing an opportune length of the fiber, the residual idler modulation can be suppressed or counteracted by an increase of optical average power. Thus, a proper choice of the transmission fiber length can considerably improve the remodulated idler characteristics. © 2012 The Royal Swedish Academy of Sciences. Source

Fernandes P.A.,Campus Universitrio Of Santiago | Fernandes P.A.,Polytechnic Institute of Porto | Salome P.M.P.,Campus Universitrio Of Santiago | Cunha A.F.D.,Campus Universitrio Of Santiago
Journal of Physics D: Applied Physics | Year: 2010

Thin films of Cu2SnS3 and Cu3SnS 4 were grown by sulfurization of dc magnetron sputtered Sn-Cu metallic precursors in a S2 atmosphere. Different maximum sulfurization temperatures were tested which allowed the study of the Cu 2SnS3 phase changes. For a temperature of 350 °C the films were composed of tetragonal (I-42m) Cu2SnS3. The films sulfurized at a maximum temperature of 400 °C presented a cubic (F-43m) Cu2SnS3 phase. On increasing the temperature up to 520 °C, the Sn content of the layer decreased and orthorhombic (Pmn21) Cu3SnS4 was formed. The phase identification and structural analysis were performed using x-ray diffraction (XRD) and electron backscattered diffraction (EBSD) analysis. Raman scattering analysis was also performed and a comparison with XRD and EBSD data allowed the assignment of peaks at 336 and 351 cm-1 for tetragonal Cu2SnS 3, 303 and 355 cm-1 for cubic Cu2SnS 3, and 318, 348 and 295 cm-1 for the Cu 3SnS4 phase. Compositional analysis was done using energy dispersive spectroscopy and induced coupled plasma analysis. Scanning electron microscopy was used to study the morphology of the layers. Transmittance and reflectance measurements permitted the estimation of absorbance and band gap. These ternary compounds present a high absorbance value close to 104 cm-1. The estimated band gap energy was 1.35 eV for tetragonal (I-42m) Cu2SnS3, 0.96 eV for cubic (F-43m) Cu 2SnS3 and 1.60 eV for orthorhombic (Pmn21) Cu 3SnS4. A hot point probe was used for the determination of semiconductor conductivity type. The results show that all the samples are p-type semiconductors. A four-point probe was used to obtain the resistivity of these samples. The resistivities for tetragonal Cu2SnS3, cubic Cu2SnS3 and orthorhombic (Pmn21) Cu 3SnS4 are 4.59 × 10-2 Ω cm, 1.26 × 10-2 Ω cm, 7.40 × 10-4 Ω cm, respectively. © 2010 IOP Publishing Ltd. Source

Muga N.J.,University of Aveiro | Muga N.J.,Campus Universitrio Of Santiago | Pinto A.N.,University of Aveiro | Pinto A.N.,Campus Universitrio Of Santiago
Journal of Lightwave Technology | Year: 2014

We propose a novel polarization demultiplexing technique for complex modulated signals using the Stokes space polarization representation of the signal samples. Polarization demultiplexing of an endless time-varying SOP signal is achieved through the adaptive estimation of the inverse rotation matrix, without the calculation of a best fitting plane. Simulation results show the effectiveness of the proposed technique, with a high convergence speed, and a good response to time-varying SOP rotations. The performance of the method is assessed through EVM calculations for frequency rotations up to 15 \murad/symbol, showing a maximum penalty of 1 dB. Moreover, the technique can incorporate an additional stage for PDL compensation without penalties in terms of EVM results and algorithm complexity. © 2012 IEEE. Source

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