Non INESC TEC publications - Indexed Articles in Journals

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    High sensitivity LPG Mach-Zehnder sensor for real-time fuel conformity analysis
    ( 2013) Osorio,JH ; Mosquera,L ; Carlos Jesus Gouveia ; Biazoli,CR ; Hayashi,JG ; Pedro Jorge ; Cordeiro,CMB
    A high sensitivity refractive index sensor based on the combination of mechanically induced long period gratings (LPG) and fiber tapers was developed for real-time fuel quality analysis. The sensor was built in a Mach-Zehnder configuration by employing a pair of in-series gratings. In order to enhance sensor sensitivity, the region between both LPGs was tapered down from 125 to 10 mu m. The system was tested by measuring water concentration in ethanol and ethanol concentration in commercial gasoline. The tapered sensor has shown an average sensitivity of 930 nm/RIU, 18 times higher than the non-tapered version. The resolution limit of the system using spectral interrogation was estimated to be 0.06% of ethanol dissolved in gasoline. For the purpose of real-time monitoring, an interrogation system based on white light interferometry (WLI) and virtual instrumentation was employed to evaluate ethanol evaporation in water, avoiding the use of spectral analysis. The WLI system, using phase tracking techniques, enabled us to record the evolution of the ethanol concentration in water with a resolution of 0.005% (v/v).
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    A new Branch and Bound method for a discrete truss topology design problem
    ( 2013) Adelaide Cerveira ; Agra,A ; Bastos,F ; Gromicho,J
    Our paper considers a classic problem in the field of Truss Topology Design, the goal of which is to determine the stiffest truss, under a given load, with a bound on the total volume and discrete requirements in the cross-sectional areas of the bars. To solve this problem we propose a new two-stage Branch and Bound algorithm. In the first stage we perform a Branch and Bound algorithm on the nodes of the structure. This is based on the following dichotomy study: either a node is in the final structure or not. In the second stage, a Branch and Bound on the bar areas is conducted. The existence or otherwise of a node in this structure is ensured by adding constraints on the cross-sectional areas of its incident bars. In practice, for reasons of stability, free bars linked at free nodes should be avoided. Therefore, if a node exists in the structure, then there must be at least two incident bars on it, unless it is a supported node. Thus, a new constraint is added, which lower bounds the sum of the cross-sectional areas of bars incident to the node. Otherwise, if a free node does not belong to the final structure, then all the bar area variables corresponding to bars incident to this node may be set to zero. These constraints are added during the first stage and lead to a tight model. We report the computational experiments conducted to test the effectiveness of this two-stage approach, enhanced by the rule to prevent free bars, as compared to a classical Branch and Bound algorithm, where branching is only performed on the bar areas.
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    Synergistic Effect between Cisplatin and Sunitinib Malate on Human Urinary Bladder-Cancer Cell Lines
    ( 2013) Arantes Rodrigues,R ; Pinto Leite,R ; Lio Gonçalves ; Palmeira,C ; Santos,L ; Colaco,A ; Oliveira,P
    The aim of this paper is to analyse sunitinib malate in vitro ability to enhance cisplatin cytotoxicity in T24, 5637, and HT1376 human urinary bladder-cancer cell lines. Cells were treated with cisplatin (3, 6, 13, and 18 mu M) and sunitinib malate (1, 2, 4, 6, and 20 mu M), either in isolation or combined, over the course of 72 hours. 3-(4,5-Dimethylthiazol-2-yl)- 2,5-diphenyl tetrazolium bromide assay, acridine orange, and monodansylcadaverine staining and flow cytometry were performed. The combination index (CI) was calculated based on the Chou and Talalay method. In isolation, cisplatin and sunitinib malate statistically (p < 0.05) decrease cell viability in all cell lines in a dose-dependent manner, with the presence of autophagic vacuoles. A cell cycle arrest in early S-phase and in G(0)/G(1) -phase was also found after exposure to cisplatin and sunitinib malate, in isolation, respectively. Treatment of urinary bladder-cancer cells with a combination of cisplatin and sunitinib malate showed a synergistic effect (CI < 1). Autophagy and apoptosis studies showed a greater incidence when the combined treatment was put into use. This hints at the possibility of a new combined therapeutic approach. If confirmed in vivo, this conjugation may provide a means of new perspectives in muscle-invasive urinary bladder cancer treatment.
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    Application of Nanotechnology in the Agro-Food Sector
    ( 2013) Lopes,CM ; José Ramiro Fernandes ; Martins Lopes,P
    Nanotechnology is an emerging field of research that has been widely applied in different scientific and engineering areas. The agro-food sector is not an exception, which considers its applicability in several areas of major interest for both consumers and producers. This review considers major concepts related to nanostructures and nano-based instruments used in the food sector, as well as their applications in agro-food products. Food safety through the use of nanosensors for pathogen detection, smart packaging, and valorisation of food products by nanoencapsulation/nanodelivery of food ingredients (e.g. flavours) are examples of important areas of nanotechnology. Consumers' apprehension regarding food stability and safety issues is also considered.
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    High-speed integrated optical logic based on the protein bacteriorhodopsin
    ( 2013) Mathesz,A ; Fabian,L ; Valkai,S ; Daniel Alexandre ; Paulo Vicente Marques ; Ormos,P ; Wolff,EK ; Der,A
    The principle of all-optical logical operations utilizing the unique nonlinear optical properties of a protein was demonstrated by a logic gate constructed from an integrated optical Mach-Zehnder interferometer as a passive structure, covered by a bacteriorhodopsin (bR) adlayer as the active element. Logical operations were based on a reversible change of the refractive index of the bR adlayer over one or both arms of the interferometer. Depending on the operating point of the interferometer, we demonstrated binary and ternary logical modes of operation. Using an ultrafast transition of the bR photocycle (BR-K), we achieved high-speed (nanosecond) logical switching. This is the fastest operation of a protein-based integrated optical logic gate that has been demonstrated so far. The results are expected to have important implications for finding novel, alternative solutions in all-optical data processing research.
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    Strong birefringence tuning of optical waveguides with femtosecond laser irradiation of bulk fused silica and single mode fibers
    ( 2013) Fernandes,LA ; Grenier,JR ; Paulo Vicente Marques ; Stewart Aitchison,J ; Herman,PR
    Birefringence tunability is demonstrated in waveguides formed in bulk fused silica and in the core of single mode fibers, by femtosecond laser writing of stress inducing tracks that are placed with different geometries around the core of the waveguides. The femtosecond laser generated stress effect was probed by the birefringence induced spectral splitting of either Bragg grating waveguides in bulk fused silica or weakly modulated, femtosecond laser induced Bragg gratings in optical fibers. Birefringence values as low as 4 × 10 -6 and up to 2 × 10-3 were obtained by controlling the fabrication conditions such as the laser pulse energy, the writing femtosecond laser polarization, the number of overwriting exposures, and the geometry of the induced stress tracks. Wave retarders are developed and characterized by a cross polarization technique to provide the spectral response of the stress induced birefringence, offering the convenient fabrication of short length and broadband in-line polarization devices. With this approach, millimeter length tracks provided 10 nm bandwidth polarization retarders in a single mode fiber and a 65 nm bandwidth retarders in bulk fused silica. © 1983-2012 IEEE.
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    Interrogation Sensing Scheme Based on a Figure-of-Eight Fiber Loop Mirror
    ( 2013) Silva,RM ; Layeghi,A ; Zibaii,MI ; Latifi,H ; José Luís Santos ; Lobo Ribeiro,ABL ; Orlando Frazão
    A fiber optic interrogation sensor scheme based on a "figure-of-eight" configuration created from a single directional 3 x 3 fiber optic coupler is proposed. Two loops are formed in each arm and one of them contains the sensing head and the other is used as reference signal. A theoretical study based on Jones matrix analysis of this fiber loop mirror combination is reported. The optical configuration is tested as an interrogation scheme for a fiber strain sensor where the spectral response arises from the combination of the reference signal modulated by the sensor signal. The strain sensor configuration shows a phase sensitivity of 6.7 +/- 4.38 x 10(-2) mrad/mu strain by linear regression.
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    Fiber laser sensor based on a phase-shifted chirped grating for acoustic sensing of partial discharges
    ( 2013) Lima,SEU ; Farias,RG ; Araujo,FM ; Ferreira,LA ; José Luís Santos ; Vladimiro Miranda ; Orlando Frazão
    Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in the high voltage apparatus. Partial discharges are a major source of insulation failure in electric power transformers, and the differentiation from other sources of acoustic emission is of the utmost importance. This paper reports the development of a new sensor concept - a fiber laser sensor based on a phase-shifted chirped fiber grating - for the acoustic emission detection of incipient faults in oil-filled power transformers. These sensors can be placed in the inner surface of the transformer tank wall, not affecting the insulation integrity of the structure and improving fault detection and location. The performance of the sensing head is characterized and compared for different surrounding media: air, water, and oil. The results obtained indicate the feasibility of this sensing approach for the industrial development of practical solutions. © 2012 The Author(s).
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    Influence of Process Parameters on the RF Sputtered GaP Thin Films
    ( 2013) Mota,DA ; Hema Chandra,GH ; Ventura,J ; Guedes,A ; Javier Cruz
    In this work, gallium phosphide thin films were deposited on glass substrates by radio frequency (RF) magnetron sputtering technique under different depositions conditions. The X-ray diffraction analysis showed a diversity of states: from amorphous in the films deposited at 175 degrees C to a nearly stoichiometric and polycrystalline films, exhibiting cubic phase with preferred orientation along (220), in the films deposited at temperatures higher than 250 degrees C. Scanning electron microscopy images revealed that all films were uniform with a smooth surface, while the energy-dispersive spectroscopy (EDS) analysis showed that there was a visible dependence on the Ga/P ratio in the deposition conditions and confirmed that a residual Ga metallic phase was presented in the surface of all the films. The Raman analysis showed the structural evolution of the GaP films was strongly dependent on the deposition conditions. The conductivity of the films was slightly dependent on the argon pressure and the rf power, but strongly dependent on the deposition temperature, mainly above 200 degrees C. The optical transmission and absorption analyses of the GaP films revealed an indirect band gap of similar to 1.70 eV in the films deposited at temperatures less than 200 degrees C, which transited to a band gap of 2.26 eV as the deposition temperature was close to 300 degrees C.
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    Oxidation of ZnO thin films during pulsed laser deposition process
    ( 2013) De Posada,E ; Moreira,L ; Javier Cruz ; Arronte,M ; Ponce,LV ; Flores,T ; Lunney,JG
    Pulsed laser deposition of ZnO thin films, using KrF laser, is analysed. The films were deposited on (001) sapphire substrates at 400 A degrees C, at two different oxygen pressures (0 center dot 3 and 0 center dot 4 mbar) and two different target-substrate distances (30 and 40 mm). It is observed that in order to obtain good quality in the photoluminescence of the films, associated with oxygen stoichiometry, it is needed to maximize the time during which the plasma remains in contact with the growing film (plasma residence time), which is achieved by selecting suitable combinations of oxygen pressures and target to substrate distances. It is also discussed that for the growth parameters used, the higher probability for ZnO films growth results from the oxidation of Zn deposited on the substrate and such process takes place during the time that the plasma is in contact with the substrate. Moreover, it is observed that maximizing the plasma residence time over the growing film reduces the rate of material deposition, favouring the surface diffusion of adatoms, which favours both Zn-O reaction and grain growth.
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    Induced polarized state in intentionally grown oxygen deficient KTaO3 thin films
    ( 2013) Mota,DA ; Romaguera Barcelay,Y ; Tkach,A ; Javier Cruz ; Vilarinho,PM ; Tavares,PB ; Agostinho Moreira,JA ; Almeida,A
    Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO2/Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K2O rich KTaO3 targets and specific deposition conditions, KTaO3-delta oxygen deficient thin films with a K/Ta = 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO3-delta thin films are under a compressive strain of 2.3% relative to KTaO3 crystals. Leakage current results reveal the presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below T-pol similar to 367 degrees C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal annealing the films in an oxygen atmosphere at a temperature above T-pol, the aforementioned polarized state is suppressed, associated with a drastic oxygen vacancies reduction emerging from annealing process. (C) 2013 AIP Publishing LLC.
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    On the improvement of strain measurements with FBG sensors embedded in unidirectional composites
    ( 2013) Pereira,G ; Frias,C ; Faria,H ; Orlando Frazão ; Marques,AT
    Optical fibre Bragg grating (FBG) sensors are now quite established and widely used in strain measurements of composites. However, insufficient understanding of the limitations of the embedment and measuring techniques often lead to inaccurate and inconclusive results. In this study, a novel method to improve the reliability and accuracy of the strain measurements on unidirectional composites using embedded FBG sensors was successfully developed. Using a carbon/epoxy prepreg system, test specimens were manufactured with longitudinally embedded FBG sensors. The combined behaviour of the sensors and the host material was characterized and a calibration rule (correction factor) was determined for the chosen material. The consistency of the results with both theoretical and empirical assumptions suggests that the proposed method is applicable to a wide range of FBG sensors and host materials.
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    Automatic Lane Segmentation in TLC Images Using the Continuous Wavelet Transform
    ( 2013) Moreira,B ; Sousa,A ; Ana Maria Mendonça ; Aurélio Campilho
    This paper describes a new methodology for lane detection in Thin-Layer Chromatography images. An approach based on the continuous wavelet transform is used to enhance the relevant lane information contained in the intensity profile obtained from image data projection. Lane detection proceeds in three phases: the first obtains a set of candidate lanes, which are validated or removed in the second phase; in the third phase, lane limits are calculated, and subtle lanes are recovered. The superior performance of the new solution was confirmed by a comparison with three other methodologies previously described in the literature.
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    Meloxicam synergistically enhances the in vitro effects of sunitinib malate on bladder-cancer cells
    ( 2013) Arantes Rodrigues,R ; Pinto Leite,R ; Lio Gonçalves ; Gaivao,I ; Colaco,A ; Oliveira,P ; Santos,L
    To evaluate the in vitro effects of sunitinib malate and meloxicam in isolation, and to analyse the ability of meloxicam to enhance the cytotoxicity of sunitinib malate in three human bladder-cancer call lines. Cell lines were treated with sunitinib malate and meloxicam, either in isolation or combined. Leishman staining, MTT method, comet assay, MDC staining and M30 CytoDEATH antibody were performed. The Chou and Talalay method was applied. Sunitinib malate and meloxicam supressed cell proliferation in bladder-cancer cells in isolation, in a concentration-dependent manner. Treatment of bladder-cancer cells with a combination of sunitinib malate and meloxicam showed a synergistic effect. When exploring the mechanism of this combination by means of comet assay, there is the suggestion that meloxicam increases sunitinib malate cytotoxicity through DNA damage. Autophagic and apoptotic studies show a greater incidence of autophagic vacuoles and early apoptotic cells when the combined treatment was put into use. In isolation, sunitinib malate and meloxicam demonstrated anti-tumor effects in our study. Furthermore, simultaneous exposure of cells to sunitinib malate and meloxicam provided a combinatorial beneficial effect. This hints at the possibility of a new combined therapeutic regimen, which could lead to improvements in the treatment of patients with bladder cancer.
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    Review of fiber-optic pressure sensors for biomedical and biomechanical applications
    ( 2013) Paulo Roriz Oliveira ; Orlando Frazão ; Lobo Ribeiro,AB ; José Luís Santos ; Simoes,JA
    As optical fibers revolutionize the way data is carried in telecommunications, the same is happening in the world of sensing. Fiber-optic sensors (FOS) rely on the principle of changing the properties of light that propagate in the fiber due to the effect of a specific physical or chemical parameter. We demonstrate the potentialities of this sensing concept to assess pressure in biomedical and biomechanical applications. FOSs are introduced after an overview of conventional sensors that are being used in the field. Pointing out their limitations, particularly as minimally invasive sensors, is also the starting point to argue FOSs are an alternative or a substitution technology. Even so, this technology will be more or less effective depending on the efforts to present more affordable turnkey solutions and peer-reviewed papers reporting in vivo experiments and clinical trials. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.JBO.18.5.050903]
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    A Review of Refractometric Sensors Based on Long Period Fibre Gratings
    ( 2013) Gaspar Rego
    In the last decade refractometric sensors have attracted an increasing interest by the scientific community due to their ability to perform ambient monitoring, to assess food quality and safety, and also to the fact that they enable the development of label free sensors in the biomedical area. These advances result, namely, from the use of long period fibre gratings in the turning points and/ or with thin films in the transition region that allows resolutions of 10(-6) to changes in the refractive index of the surrounding medium. Resolutions exceeding 10(-8) can also be achieved when long period fibre gratings are combined with evanescent field based devices. This paper reviews the recent path towards the development of ultrahigh sensitive optical fibre refractometric sensors.
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    Pushouts in Software Architecture Design
    ( 2013) Riche,TL ; Rui Carlos Gonçalves ; Marker,B ; Batory,D
    A classical approach to program derivation is to progressively extend a simple specification and then incrementally refine it to an implementation. We claim this approach is hard or impractical when reverse engineering legacy software architectures. We present a case study that shows optimizations and pushouts-in addition to refinements and extensions-are essential for practical stepwise development of complex software architectures.
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    Modulation instability-induced fading in phase-sensitive optical time-domain reflectometry
    ( 2013) Martins,HF ; Martin Lopez,S ; Corredera,P ; Salgado,P ; Orlando Frazão ; Gonzalez Herraez,M
    Phase-sensitive optical time-domain reflectometry (phi OTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. We show in this Letter that modulation instability (MI) can induce a position-dependent signal fading in long-range phi OTDR over conventional optical fibers. This fading leads to a complete masking of the interference signal recorded at certain positions and therefore to a sensitivity loss at these positions. We illustrate this effect both theoretically and experimentally. While this effect is detrimental in the context of distributed vibration analysis using phi OTDR, we also believe that the technique provides a clear and insightful way to evidence the Fermi-Pasta-Ulam recurrence associated with the MI process. (C) 2013 Optical Society of America
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    Room temperature structure and multiferroic properties in Bi0.7La0.3FeO3 ceramics
    ( 2013) Carvalho,TT ; José Ramiro Fernandes ; Perez de la Cruz,JP ; Vidal,JV ; Sobolev,NA ; Figueiras,F ; Das,S ; Amaral,VS ; Almeida,A ; Agostinho Moreira,JA ; Tavares,PB
    Single phase Bi0.7La0.3FeO3 ceramic samples were successfully synthesized by sol-gel combustion and co-precipitation methods, performing a final sintering at 820-870 degrees C from 10 up to 180 min. Rietveld refinements of the XRD data detected small satellite peaks that were successfully indexed by an incommensurated modulated structure model. Lanthanum doping improves magnetic response, reduces the leakage current and dielectric losses. The piezoelectric coefficient was reported for the first time in the Bi0.7La0.3FeO3 composition.