2017
Autores
Santos, DF; Guerreiro, A; Baptista, JM;
Publicação
IEEE SENSORS JOURNAL
Abstract
This paper presents an optical fiber sensor, that uses surface plasmon resonance on metallic wires to directly and simultaneously measure both the refractive index and the temperature. The sensor is constituted by gold wires on a D-type fiber engineered, using numerical simulations based on the finite-element method to support plasmon modes with strong dependencies to either one of the measured parameters. In particular, the influence of the temperature on the structure of the plasmon modes results from contributions from the thermooptic effect in the fiber core and sensing layer, and phononelectron scattering along with electron-electron scattering in the metal wire. The performance of the sensor is evaluated in terms of its sensitivity and resolution.
2017
Autores
Silva, NA; Ferreira, TD; Costa, JC; Gomes, M; Alves, RA; Guerreiro, A;
Publicação
QUANTUM PHOTONIC DEVICES
Abstract
The realization of tabletop optical analogue experiments of superfluidity relies on the engineering of suitable optical media, with tailored optical properties. This work shows how quantum atomic optical systems can be used to develop highly tunable optical media, with localized control of both linear and nonlinear susceptibility. Introducing the hydrodynamic description of light, the superfluidity of light in these atomic media is investigated through GPU-enhanced numerical simulations, with the numeric observation of the superfluidic signature of suppressed scattering through a defect.
2017
Autores
Gouveia, CAJ; Coelho, L; Franco, MAR;
Publicação
2017 25TH INTERNATIONAL CONFERENCE ON OPTICAL FIBER SENSORS (OFS)
Abstract
The design and modelling of a novel magnetic field sensor based on a long period fiber grating coated with a thin film of N doped ZnO is reported. The parameters of both, the grating and the thin film were carefully chosen to operate in the transition mode and near to the dispersion turning point. At this point, an LPFG shows its maximum sensitivity to external refractive index variations. The magnetic field induces variations in the coating refractive index, which changes the effective refractive index of the cladding mode and the consequent spectral response. In this work a sensitivity to the surrounding magnetic field of 2.9 nm/mT is reported with a maximum theoretical resolution of 2 mu T.
2017
Autores
Saraiva, C; Vasconcelos, H; de Almeida, JMMM;
Publicação
INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY
Abstract
The aim of this work was to investigate the potential of Fourier transform infrared spectroscopy (FTIR) to detect and predict the bacterial load of salmon fillets (Salmo salar) stored at 3, 8 and 30 degrees C under three packaging conditions: air packaging (AP) and two modified atmospheres constituted by a mixture of 50%N-2/40%CO2/10%O-2 with lemon juice (MAPL) and without lemon juice (MAP). Fresh salmon samples were periodically examined for total viable counts (TVC), specific spoilage organisms (SSO) counts, pH, FTIR and sensory assessment of freshness. Principal components analysis (PCA) allowed identification of the wavenumbers potentially correlated with the spoilage process. Linear discriminant analysis (LDA) of infrared spectral data was performed to support sensory data and to accurately identify samples freshness. The effect of the packaging atmospheres was assessed by microbial enumeration and LDA was used to determine sample packaging from the measured infrared spectra. It was verified that modified atmospheres can decrease significantly the bacterial load of fresh salmon. Lemon juice combined with MAP showed a more pronounced delay in the growth of Brochothrix thermosphacta, Photobacterium phosphoreum, psychrotrophs and H2S producers. Partial least squares regression (PLS-R) allowed estimates of TVC and psychrotrophs, lactic acid bacteria, molds and yeasts, Brochothrix thermosphacta, Enterobacteriaceae, Pseudomonas spp. and H2S producer counts from the infrared spectral data: For TVC, the root mean square error of prediction (RMSEP) value was 0.78 log cfu g(-1) for an external set of samples. According to the results, FTIR can be used as a reliable, accurate and fast method for real time freshness evaluation of salmon fillets stored under different temperatures and packaging atmospheres.
2017
Autores
Gouveia, AR; Alves, M; de Almeida, JMMM; Monteiro Silva, F; Gonzalez Aguilar, G; Silva, JA; Saraiva, C;
Publicação
JOURNAL OF FOOD PROCESSING AND PRESERVATION
Abstract
Sous vide cook-chill (SVCC) is characterized by vacuum-packaging raw or partially prepared foods before pasteurization, followed by rapid chilling and storage below 3C. The application of essential oils (EOs) to food products is a suitable strategy to control pathogens and to extend their shelf life by reducing microbial levels and oxidative processes. The aim of this study was to evaluate the efficacy of Rosmarinus officinalis L. (rosemary) and Thymus vulgaris L. (thyme) EOs against Listeria monocytogenes ATCC 679, inoculated in beef processed by SVCC stored at 2 and 8C for 1, 2, 3, 7, 14, 21 and 28 days. The composition of EOs was identified by gas chromatography-mass spectrometry analysis. The main compounds identified in rosemary EO were eucalyptol (13.05%), camphor (8.93%), verbenone (8.58%), endo-borneol (7.87%) and alpha-pinene (6.78%) and in thyme EO were linalool (18.18%), thymol (7.48%), limonene (6.49%), endo-borneol (5.86%) and terpinen-4-ol (5.66%). Using the minimum inhibitory concentration (MIC) method, L. monocytogenes was inhibited at 3.9 mu L/mL to thyme EO and at 62.5 mu L/mL to rosemary EO. Beef samples of M. longissimus thoracis et lumborum were packaged in bags, inoculated and one of each EO was added at MIC values. Bags were vacuum-sealed and samples were processed at 55C/65 min for 3log(10) CFU/g reduction. A reduction of the counts of L. monocytogenes was observed in all samples at 2C. At 8C counts of L. monocytogenes were almost similar in control samples and those with thyme EO with an increase of themicrobial counts since day 7. Inversely, counts of L. monocytogenes in beef samples with rosemary EO stored at 2 and 8C decreased about 2 log(10) CFU. These results support the possibility of using rosemary EO as natural preservative due to its antimicrobial effect against L. monocytogenes. Also, our results confirm that an adequate chilling storage is essential to guarantee the safety of SVCC product regarding L. monocytogenes to avoid foodborne outbreaks.
2017
Autores
Mendes, JP; Esperanca, JMSS; Medeiros, MJ; Pawlicka, A; Silva, MM;
Publicação
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Abstract
New polymer electrolytes (PEs), potentially interesting for solid-state electrochemical devices applications, were synthesized by a solvent casting method using pectin and ionic liquid (IL) N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([N-1 1 1 2(OH)] [NTf2]. The resulting electrolytes besides being moderately homogenous and thermally stable below 155 degrees C, they also exhibited good mechanical properties. The SPE membranes were analyzed by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and complex impedance spectroscopy.
The access to the final selection minute is only available to applicants.
Please check the confirmation e-mail of your application to obtain the access code.