Percorrer por data de Publicação, começado por "2015-12"
A mostrar 1 - 10 de 79
Resultados por página
Opções de ordenação
- Transition to the maternal role in women with addiction problems to psychoactive substances: conceptual mapPublication . Henriques, Carolina; Botelho, Maria Antonia Rebelo; Catarino, HelenaThe transition to motherhood is seen as a phenomenon where are interwoven multiple variables, where the experience of being a mother can be so significant andfull of pleasure, as associated with suffering and unhappiness processes.If we associate this phenomenon, itself multidimensional, the problem of adding the psychoactive substances, the spectrum of its complexity increases, whereas the mother experiences a set of changes associated with pregnancy, childbirth and postpartum, at the same time with their behaviourto addition to psychoactive substances. Looking for the integration of the concepts involved in the problems of transition to the maternal role in women with addition problems to psychoactive substances, we used the conceptual map as a basic tool for the organization of scientific knowledge in the field of study. We conclude from its analysis, that women with addition problems to psychoactive substances, in the process of transition to the maternal role, experience adjustment processes of adaptation and transition, where their past contexts, present and future perspectives converge maternal identity, as the individual characteristics of each woman (self-esteem, personal integrity and self-confidence).
- Reference picture selection using checkerboard pattern for resilient video codingPublication . Carreira, J.; Assunção, P.; Faria, S.; Ekmekcioglu, E.; Kondoz, A.; Lim, H.The improved compression efficiency achieved by the High Efficiency Video Coding (HEVC) standard has the counter-effect of decreasing error resilience in transmission over error-prone channels. To increase the error resilience of HEVC streams, this paper proposes a checkerboard reference picture selection method in order to reduce the prediction mismatch at the decoder in case of frame losses. The proposed approach not only allows to reduce the error propagation at the decoder, but also enhances the quality of reconstructed frames by selectively constraining the choice of reference pictures used for temporal prediction. The underlying approach is to increase the amount of accurate temporal information at the decoder when transmission errors occur, to improve the video quality by using an efficient combination of diverse motion fields. The proposed method compensates for the small loss of coding efficiency at frame loss rates as low as 3%. For a single frame-loss event the proposed method can achieve up to 2 dB of gain in the affected frames and an average quality gain of 0.84 dB for different error prone conditions.
- Complexity-Aware High Efficiency Video CodingPublication . Corrêa, Guilherme; Assunção, Pedro; Agostini, Luciano; Cruz, Luis A. da SilvaThis book discusses computational complexity of High Efficiency Video Coding (HEVC) encoders with coverage extending from the analysis of HEVC compression efficiency and computational complexity to the reduction and scaling of its encoding complexity. After an introduction to the topic and a review of the state-of-the-art research in the field, the authors provide a detailed analysis of the HEVC encoding tools compression efficiency and computational complexity. Readers will benefit from a set of algorithms for scaling the computational complexity of HEVC encoders, all of which take advantage from the flexibility of the frame partitioning structures allowed by the standard. The authors also provide a set of early termination methods based on data mining and machine learning techniques, which are able to reduce the computational complexity required to find the best frame partitioning structures. The applicability of the proposed methods is finally exemplified with an encoding time control system that employs the best complexity reduction and scaling methods presented throughout the book. The methods presented in this book are especially useful in power-constrained, portable multimedia devices to reduce energy consumption and to extend battery life. They can also be applied to portable and non-portable multimedia devices operating in real time with limited computational resources.
- Complexity Analysis of HEVC Decoding for Multi-core PlatformsPublication . Cordeiro, Paulo J.; Assunção, Pedro; Gómez-Pulido, Juan A.The High Efficiency Video Coding (HEVC) is the latest standard, providing the same quality as its predecessor H.264/AVC at about half of the bit-rate. An increasing demand for higher quality and better resolutions in mobile applications require the use of more efficient video codecs, but the high computational complexity of HEVC poses problems to resource-constrained devices and portable equipment with limited batery-life. Despite the fact that video coding complexity is much higher than decoding, in most user devices, video decoding is used more often than encoding, thus particular attention must also be given to HEVC decoders. This paper presents an experimental study and complexity analysis of the HEVC decoder’s behaviour when decoding 4k ultra high definition (UHD) and HD video sequences on multi-core platforms, such as those of the most recent mobile devices. It is shown that when tile partitioning is used, different tiles have different decoding complexities. These findings are relevant for devising dynamic tile partitioning schemes capable of achieving load balancing in video decoders running on multi-core platforms.
- Fatigue behaviour of epoxy-steel single lap joints under variable frequencyPublication . Reis, P.N.B.; Monteiro, J.F.R.; Pereira, António; Ferreira, J.F.R.; J.D.M. CostaThis work investigates the loading frequency effects on the fatigue behaviour of adhesively-bonded steel lap joints. S-N diagrams of fatigue tests, under constant amplitude loading, were obtained for frequencies ranging between 2 and 40 Hz. The fatigue life for variable frequency tests was estimated based on constant frequency S-N curves, using a linear cumulative damage rule. It is possible to conclude that, for the higher shear stresses, the frequency presents only a marginal effect on fatigue life. On the other hand, for the lower shear stresses, the fatigue life of the adhesive joints is very dependant on the frequency level. Good correlations were obtained between fatigue life predictions and experimental results. © 2015 Elsevier Ltd. All rights reserved.
- Geometric transforms and reference picture list optimization for efficient disparity compensationPublication . Ricardo J. S. Monteiro; M. M. Rodrigues, Nuno; Faria, SergioThis paper presents a method to increase the efficiency of the disparity compensation process performed by state-of-the-art video coding extensions for 3D and multiview. Disparity compensation relies traditionally on a block matching algorithm limited to two degrees of freedom, that in many cases does not adequately address the disparity created by the camera arrays. The proposed method is combined with MV-HEVC in order to improve the efficiency of inter-frame prediction, by generating additional reference pictures, using 3D scene information. The new geometrically compensated pictures are chosen and reordered based on their usefulness for prediction and associated cost in the encoding process. When compared to MV-HEVC, the proposed scheme is able to achieve bitrate savings of up to 3.19% for convergent camera arrangements and 2.41% for parallel camera arrangements.
- Contributions to lossless coding of medical images using minimum rate predictorsPublication . Joao M. Santos; Guarda, André; M. M. Rodrigues, Nuno; Faria, SergioMedical imaging compression is experiencing a growth in terms of usage and image resolution, namely in diagnostics systems that require a large set of images, like MRI or CT. Furthermore, legal and diagnosis restrictions impose the use of lossless compression and data archival for several years. These facts create a demand for more efficient compression tools, used for archiving and communication. In this work, we first evaluate the performance of traditional medical image compression algorithms against that of recent state of the art lossless image encoders. We then propose a method to improve the Minimum Rate Predictors lossless encoder, by exploiting inter picture redundancy in volumetric anatomical images. Results show that the proposed method is more efficient than state of the art encoders, such as HEVC, by about 28.8%, and achieves a gain of up to 57.8% in compression ratio when compared with traditional methods.
- Effect of adherends and environment on static and transverse impact response of adhesive lap jointsPublication . Reis, P.N.B.; Soares, J.R.L.; Pereira, António; Ferreira, J.A.M.Impact response of adhesive joints has received limited attention compared to quasi-static loading. On the other hand, there are very few studies combining moisture and its effect on the impact strength. Therefore, the present paper aims to study the effect of moisture on the tensile and impact strength of single lap joints with different adherends (high limit elastic steel and a commercial composite). It was possible to conclude that adhesive joints with steel adherends are very sensitive to the environment and exposure time. For adhesive joints with composite adherends, the water showed a marginal effect. A marked hygrothermal effect was observed for all joints. For impact loads the environment effect is similar, but much more severe than that observed in tensile tests. For both tests, adhesive failures occurred for adhesive joints with steel adherends and delaminations for joints involving composite.
- On the mechanical properties of PLC–bioactive glass scaffolds fabricated via BioExtrusionPublication . Fiedler, T.; Videira, A.C.; Bartolo, Paulo; Strauch, M.; Murch, G.E.; Ferreira, J.M.F.This paper addresses the mechanical characterization of polycaprolactone (PCL)–bioglass (FastOs®BG) composites and scaffolds intended for use in tissue engineering. Tissue engineering scaffolds support the self-healing mechanism of the human body and promote the regrowth of damaged tissue. These implants can dissolve after successful tissue regeneration minimising the immune reaction and the need for revision surgery. However, their mechanical properties should match surrounding tissue in order to avoid strain concentration and possible separation at the interface. Therefore, an extensive experimental testing programme of this advanced material using uni-axial compressive testing was conducted. Tests were performed at low strain rates corresponding to quasi-static loading conditions. The initial elastic gradient, plateau stress and densification strain were obtained. Tested specimens varied according to their average density and material composition. In total, four groups of solid and robocast porous PCL samples containing 0, 20, 30, and 35% bioglass, respectively were tested. The addition of bioglass was found to slightly decrease the initial elastic gradient and the plateau stress of the biomaterial scaffolds.
- Searching for the corner seismic moment in worldwide dataPublication . Felgueiras, Miguel; Santos, Rui; Oliveira Martins, João PauloIn this paper the existence of the corner frequency value for the seismic moment distribution is investigated, analysing worldwide data. Pareto based distributions, usually considered as the most suitable to this type of data, are fitted to the most recent data, available in a global earthquake catalog. Despite the undeniable finite nature of the seismic moment data, we conclude that no corner frequency can be established considering the available data set. © 2015 AIP Publishing LLC.