Paiva C.R.,University of Lisbon |
Matos S.A.,Institute Telecomunicaces
IEEE Transactions on Antennas and Propagation | Year: 2012
The perfect electromagnetic conductor (PEMC) was introduced as an observer-independent axion medium that generalizes the concepts of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). Following the original boundary definition, its 3-D medium definition corresponds to a 4-D representation that is, actually, observer-dependent (i.e., it is not isotropic for the whole class of inertial observers), leading to a nonunique characterization of the electromagnetic field inside. This characterization of the PEMC, then, violates the boundary conditionsunless some extraneous waves, called metafields, are surgically extracted from the final solution. In this paper, using spacetime algebra, we define the PEMC as the unique limit of the most general class of isotropic media in Minkowskian spacetime, which we call Minkowskian isotropic media (MIM). An MIM is actually a dilaton-axion medium. Its isotropy is a Lorentz invariant characterization: It is an observer-independent property, contrary to isotropy in 3-D Gibbsian characterization. Hence, a more natural definition of a PEMC is herein presented: It leads to a unique electromagnetic field in its interior; it corresponds, though, to the same original boundary definition. This new approach is applied to the analysis of an air-MIM interface that, as a particular case, reduces to an air-PEMC interface. © 1963-2012 IEEE.
Postolache G.,University of Lisbon |
Oliveira M.,Hospital Santa Marta |
Rocha I.,Hospital Santa Marta |
Girao P.S.,University of Lisbon |
Postolache O.,Institute Telecomunicaces
Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS | Year: 2011
In this paper Heart Rate Variability (HRV) and Blood Pressure Variability (BPV) were analyzed before the onset of cardiac arrhythmia in order to derive markers for short-term forecasting. The (a) coherence between systolic blood pressure (SBP) and cardiac oscillations in low-frequency (LF) and high-frequency (HF) band; (b) fluctuations of phase; (c) HRV and BPV as a LF power and HF power in frequency and time-frequency domain; (d) transfer function analysis of cardiovascular signals were analyzed. Arrhythmia was preceded by: a) lower coherence; b) increase in fluctuations of phase between signals; c) higher spectral energy associated with respiratory frequency in blood pressure signal; d) raise of sympathetic outflow to the heart; e) decreased HRV. Cardiac arrhythmia was characterized mainly by an increase in LF power of blood pressure, cardiac signal and transfer function. During self-termination of arrhythmia a larger increased in total BPV and HRV was recorded. These results suggest that important information about both neuronal cardiovascular control and risk for spontaneous arrhythmia can be provided by combined analysis of frequency, phase, and time-frequency analysis of blood pressure and cardiac oscillation. © 2011 IEEE.
Cassa M.B.,University of Brescia |
Naccari M.,Institute Telecomunicaces |
Pereira F.,Institute Telecomunicaces |
Pereira F.,University of Lisbon
2012 Picture Coding Symposium, PCS 2012, Proceedings | Year: 2012
The under development High Efficiency Video Coding (HEVC) standard employs several powerful coding tools to obtain improved compression efficiency regarding the state-of-the-art H.264/AVC standard. To efficiently exploit the temporal and spatial redundancies, HEVC adopts a very flexible quadtree coding structure, allowing the encoder to use a block partition better matching the image features. The best combination of HEVC block partitioning and coding modes is found by means of a rate distortion optimization process. During this minimization, the encoder tests all the possible coding modes and block partitions and keeps those providing the smallest RD cost. Due to the large number of available modes and partitions, the minimization involves extremely high complexity, which may not be suitable for real-time application scenarios. To reduce the complexity, two novel fast RDO techniques are proposed in this paper: Top Skip and Early Termination. The experimental evaluation reveals that the proposed techniques significantly reduce the encoding time, notably up to 45% regarding the high complexity HEVC reference software codec, with a negligible quality loss never larger than 0.1 dB. © 2012 IEEE.
Guenda L.,Institute Telecomunicaces |
Collado A.,Catalonia Technology Center of Telecomunications |
Carvalho N.B.,Institute Telecomunicaces |
Georgiadis A.,Catalonia Technology Center of Telecomunications |
Niotaki K.,Aristotle University of Thessaloniki
RWW 2012 - Proceedings: IEEE Radio and Wireless Symposium, RWS 2012 | Year: 2012
This paper presents a description of a data-base structure that can be used for electromagnetic energy harvesting information by gather energy footprints and relate them with GPS information. The paper describes the information system architecture that is behind the data-base structure and it is expected that it will become a source of information around the world on energy harvesting. Moreover an energy harvesting probe based on Android devices is also presented. © 2012 IEEE.
Andre P.S.,Institute Telecomunicaces |
Andre P.S.,University of Aveiro |
Domingues F.,Institute Telecomunicaces |
Granada M.,University of Aveiro
2011 Conference on Lasers and Electro-Optics: Laser Science to Photonic Applications, CLEO 2011 | Year: 2011
The effect of the maritime environment on the aging of optical fibers coatings was studied. The obtained stress decay rate was 29.05 days, however, this value is higher than for a pure water saturate environment. © 2011 OSA.
Khalil G.E.,University of Sheffield |
Khalil G.E.,Cairo University |
Adawi A.M.,University of Sheffield |
Adawi A.M.,University of Hull |
And 7 more authors.
Journal of Physical Chemistry B | Year: 2011
We study the thiophene-based oligomer poly[2,7-(9,9-bis(2′- ethylhexyl)fluorene)-alt-2,5-terthiophene] (PF3T) in solution and when dispersed at low concentration into a polynorbornene matrix. We find that at high concentration in solution the 0-0 electronic transition observed in fluorescence is suppressed, a result indicative of the formation of weakly coupled H-aggregates. At low concentration in a polymer matrix, emission from both single molecules and molecular aggregates is observed. We find that the fluorescence spectra of most PF3T emitters are composed of a number of relatively narrow emission features, indicating that the emission usually occurs from multiple chromophores. A small number of PF3T molecules are however characterized by single chromophore emission, spectral blinking, and narrowed emission peaks. © 2011 American Chemical Society.
Caleiro C.,Institute Telecomunicaces |
Goncalves R.,New University of Lisbon
Fundamenta Informaticae | Year: 2011
Logical matrices are widely accepted as the semantic structures that most naturally fit the traditional approach to algebraic logic. The behavioral approach to the algebraization of logics extends the applicability of the traditional methods of algebraic logic to a wider range of logical systems, possibly encompassing many-sorted languages and non-truth-functional phenomena. However, as one needs to work with behavioral congruences, matrix semantics are unsuited to the behavioral setting. In , a promising version of algebraic valuation semantics was proposed in order to fill in this gap. Herein, we define the class of valuations that should be canonically associated to a logic, and we show, by means of new meaningful bridge results, how it is related to the behaviorally equivalent algebraic semantics of a behaviorally algebraizable logic.
Cernigliaro G.,Technical University of Madrid |
Naccari M.,Institute Telecomunicaces |
Jaureguizar F.,Technical University of Madrid |
Cabrera J.,Technical University of Madrid |
Garcia N.,Technical University of Madrid
2012 Picture Coding Symposium, PCS 2012, Proceedings | Year: 2012
A novel scheme for depth sequences compression, based on a perceptual coding algorithm, is proposed. A depth sequence describes the object position in the 3D scene, and is used, in Free Viewpoint Video, for the generation of synthetic video sequences. In perceptual video coding the human visual system characteristics are exploited to improve the compression efficiency. As depth sequences are never shown, the perceptual video coding, assessed over them, is not effective. The proposed algorithm is based on a novel perceptual rate distortion optimization process, assessed over the perceptual distortion of the rendered views generated through the encoded depth sequences. The experimental results show the effectiveness of the proposed method, able to obtain a very considerable improvement of the rendered view perceptual quality. © 2012 IEEE.
Candeias S.,Institute Telecomunicaces |
Perdigao F.,Institute Telecomunicaces |
Perdigao F.,University of Coimbra
Clinical Linguistics and Phonetics | Year: 2010
The goal of this work is to investigate whether children with speech dysfunctions (SD) show a deficit in planning some Portuguese syllable structures (PSS) in continuous speech production. Knowledge of which aspects of speech production are affected by SD is necessary for efficient improvement in the therapy techniques. The case-study is focused on PSS as C1C2V syllable sequences (consonant-consonant-vowel), in which C2 is [l] or [r]. To identify specific speech patterns that are sensitive to SD, coarticulation effects using formant trajectories, intensity, and durational structure are investigated. To explore the characteristics of continuous speech processes in SD speech output, the methodology uses acoustic analysis. Preliminary findings show systematic specific coarticulation in the child with SD when compared to the normal speech (NS) child. This also suggests that the traditional focus on a single word production in the SD assessment needs to be modified to allow more detailed consideration of speech production in continuous speech. It is the purpose of the authors in the future to develop an application that can be an optimal start for SD treatmentcounselling programmes. The work reported here proves the importance of clinic linguistic knowledge in that way. This study is the result of a multidisciplinary-team whose work allies linguist, clinical therapy and engineering knowledge. © 2010 Informa UK Ltd.
Costa-Santos C.,University of Porto |
Costa-Santos C.,Center for Research in Health Technologies and Information Systems |
Antunes L.,University of Porto |
Antunes L.,Institute Telecomunicaces |
And 3 more authors.
Annals of Epidemiology | Year: 2010
Purpose: Disagreement on the interpretation of diagnostic tests and clinical decisions remains an important problem in medicine. As no strategy to assess agreement seems to be fail-safe to compare the degree of agreement, or disagreement, we propose a new information-based approach to assess disagreement. Methods: The sum over all logarithms of possible outcomes of a variable is a valid measure of the amount of information contained in the variable. The proposed measure is based on the amount of information contained in the differences between two observations. This measure is normalized and satisfies the flowing properties: it is a metric, scaled invariant and it has differential weighting. Results: Two real examples and a simulation were used to illustrate the usefulness of the proposed measure to compare the degree of disagreement. Conclusions: Used as complement to the existing methods, we believe our approach can be useful to compare the degree of disagreement among different populations. © 2010 Elsevier Inc.