Percorrer por data de Publicação, começado por "2013-06"
A mostrar 1 - 10 de 14
Resultados por página
Opções de ordenação
- Rethinking the boundaries of labour law regarding the need of regulation of independent workPublication . Lambelho, AnaThe aim of this research is, based on the analysis of several articles of Portuguese Labour Code regarding independent work, in order to prevent fraudulent situations, to reflect about an eventual need of rethinking the boundaries of labour law in a double sense: i) whether the legal subordination must continue to be the normative axis of Labour Law, despite the changing forms of productive organization; ii) whether the scope of Labour Law should be extended to situations where there is no legal subordination but where there are other forms of dependence. The urgency of the first issue comes from the fact that the legal subordination is a notion that comes already from the times of capitalist production. Outsourcing and the business networking organization enhanced by new technologies, implying a bigger segmentation of the attributes and responsibilities of the employer, changed the paradigm on which rested the legal subordination, either from the side of who holds the power of direction, as from the side of who must obey. The legal subordination presupposes a "dominant social type" which seems to be called into question, or at least changed, by new forms of business organization. Although changes in the figures of the employer and the worker are impeding implementation and operationalization of that concept, we understand that it is endowed with sufficient elasticity to remain the distinctive element of the employment relationship. Regarding the second question, we think the Labour Law does not provide adequate legal protection to independent work neither to economically dependent autonomous work, although we defend a specific regulation of these last two types of work.
- Complex Boosts: A Hermitian Clifford Algebra ApproachPublication . Ferreira, Milton; Sommen, FranciscusThe aim of this paper is to study complex boosts in complex Minkowski space-time that preserves the Hermitian norm. Starting from the spin group Spin$^+(2n,2m,\bkR)$ in the real Minkowski space $\bkR^{2n,2m}$ we construct a Clifford realization of the pseudo-unitary group U$(n,m)$ using the space-time Witt basis in the framework of Hermitian Clifford algebra. Restricting to the case of one complex time direction we derive a general formula for a complex boost in an arbitrary complex direction and its $KAK-$decomposition, generalizing the well-known formula of a real boost in an arbitrary real direction. In the end we derive the complex Einstein velocity addition law for complex relativistic velocities, by the projective model of hyperbolic $n-$space.
- Objective quality prediction model for lost frames in 3D video over TSPublication . Feitor, Bruno; Assunção, Pedro; Soares, João; Cruz, Luís; Marinheiro, RuiThis paper proposes an objective model to predict the quality of lost frames in 3D video streams. The model is based only on header information from three different packet-layer levels: Network Abstraction Layer (NAL), Packetised Elementary Streams (PES) and Transport Stream (TS). Transmission errors leading to undecodable TS packets are assumed to result in frame loss. The proposed method estimates the size of the lost frames, which is used as a model parameter to predict their objective quality measured as the Structural Similarity Index Metric (SSIM). The results show that SSIM of missing stereoscopic frames in 3D coded video can be predicted with Root Mean Square Error (RMSE) accuracy of about 0.1 and Pearson correlation coefficient of 0.8, taking the SSIM of uncorrupted frames as reference. It is concluded that the proposed model is capable of estimating the SSIM quite accurately using only the lost frames estimated sizes.
- 3D video shot boundary detection based on clustering of depth-temporal featuresPublication . Ferreira, Lino; Assunção, Pedro; Cruz, Luis A. da SilvaThis paper proposes an algorithm for automatic detection of 3D video shots with different perceptual features. The proposed algorithm is able to identify distinct three-dimensional visual scenes by detecting 3D video shot boundaries based on clustering of depth-temporal features. A combination of texture variation along the temporal dimension and depth variance is used by K-means clustering to find the stereo frames which comprised the 3D scene boundaries. An important characteristic of the proposed algorithm in comparison with others published in the literature for temporal segmentation of classic 2D video is that no thresholds are used in the decision processes neither training data sets. The experimental results show that the proposed method is capable of achieving high recall (e.g., 0.95) and precision rate (e.g., 1.0) in video sequences with both sharp and smooth 3D scene transitions.
- Sustainable energy for plastic industry plantPublication . Galvão, João; Moreira, Licínio; Leitão, Sérgio; Silva, Élson; Neto, MárioThis research intends to reduce energy consumption in a plastic film industrial unit. Trough the development of a new energy model focused on self renewable energy production and energy management in some sectors, such as lighting and compressed air. It is expected that this model leads to energy savings with environmental advantages (lower greenhouse gases emission). This may grant access to eco-sustainable certifications/awards as a factor of competitiveness, as well as economic benefits. The methodology followed to design the new energy model was developed from an energy audit to characterize the existing consumptions and use of energy.
- A comparative study of different approaches using an outranking relation in a multi-objective evolutionary algorithmPublication . Oliveira, Eunice; Antunes, Carlos Henggeler; Gomes, ÁlvaroThis paper presents a comparative analysis of three versions of an evolutionary algorithm in which the decision maker’s preferences are incorporated using an outranking relation and preference parameters associated with the ELECTRE TRI method. The aim is using the preference information supplied by the decision maker to guide the search process to the regions where solutions more in accordance with his/ her preferences are located, thus narrowing the scope of the search and reducing the computational effort. An example dealing with a pertinent problem in electrical distribution network is used to compare the different versions of the algorithm and illustrate how meaningful information can be elicited from a decision maker and used in the operational framework of an evolutionary algorithm to provide decision support in real-world problems.
- Talitrid and Tylid crustaceans bioecology as a tool to monitor and assess sandy beaches’ ecological quality conditionPublication . Gonçalves, Sílvia C.; Anastácio, Pedro M.; Marques, João C.In the last decades, the sharp increase of human activities on sandy beaches has introduced several detrimental impacts on these ecosystems, highlighting the importance of developing environmental quality assessments and sustainable management and protection plans for these environments. The study of key species at the population level represents an adequate and important approach to the ecosystem's ecological quality if the impacts of environmental disturbances, namely derived from human activities, are to be assessed. Talitrid and Tylid crustaceans often form abundant populations in temperate exposed sandy beaches, and might represent the bulk of the macrofaunal communities. In the present case study, the comparison of distinct Talitrid and Tylid populations on Atlantic (Portugal) and Mediterranean (Italy and Tunisia) beaches allowed to assess the adaptation of these animals on local and macro scale scenarios and evaluate the importance of bioecological studies as auxiliary tools in environmental monitoring and in the ecological quality assessment of sandy beaches. The results revealed that Talitrid and Tylid populations have a strong plasticity over geographic gradients and to local environments, presenting a high degree of variation on population ecology, namely latitudinal clines on several life history traits. Also, since the studies were performed on sandy beaches with similar degrees of exposure to wave action and low degrees of human disturbance, the present work may play a relevant role as reference knowledge in environmental monitoring studies and as an ecological quality assessment tool that might be used to evaluate the impacts of environmental disturbances on sandy beach ecosystems, namely from human origin.
- Efficient depth error concealment for 3D video over error-prone channelsPublication . Marcelino, S.; Assunção, P.; Faria, Sérgio M. M. de; Soares, S.This paper addresses the problem of multivew videoplus-depth (MVD) decoding with corrupted depth maps due to transmission errors. A method for spatial error concealment of depth maps in MVD is proposed to efficiently recover lost blocks. The proposed method relies on the colour image and geometric curve fitting for accurate reconstruction of the lost contour segments in the corresponding depth map areas. Such reconstructed depth map contours are then used as boundaries at different depth planes to recover the missing depth values through weighted interpolation. The method performance is evaluated by the objective quality (PSNR) of the synthesised views. Images decoded with the reconstructed depth maps are compared with those of a reference method based on bidirectional interpolation. The proposed method exhibits PSNR gains up to 1.66dB higher than the reference one and better performance is consistently achieved for different visual content.
- Adaptações dos processos de reconhecimento, validação e certificação de competências a alunos surdos : um estudo de casoPublication . Roussos, Cecília Maria Soares da Silva; Barreto, Maria Antónia Belchior Ferreira; Santos, Tânia Cristina Simões de Matos dos
- Complexation and DFT studies of lanthanide ions by (2-pyridylmethoxy)homooxacalixarene derivativesPublication . Marcos, Paula M.; Teixeira, Filipa A.; Segurado, Manuel A.P.; Ascenso, José R.; Bernardino, Raul; Cragg, Peter J.; Michel, Sylvia; Hubscher-Bruder, Véronique; Arnaud-Neu, FrançoiseThe binding of lanthanide cations by 2-pyridylmethoxy derivatives of p-tert-butyldihomooxacalix[4]arene (1b), in the cone conformation, and p-tert-butylhexahomotrioxacalix[3]arene (2b), in both cone and partial cone conformations, was studied. These properties were assessed by extraction studies of the metal picrates from water into dichloromethane and stability constant measurements in methanol and acetonitrile, using spectrophotometric and microcalorimetric techniques. Proton NMR titrations with La3+ and Yb3+ cations were done in order to get information on the binding sites. Computational methods (density functional theory (DFT) calculations) were also used to complement the NMR data. The p-tert-butylcalix[4]arene analogue (3b) was also studied, and the results of the four ligands were compared. Partial cone-2b is the best extractant for lanthanide ions, showing some preference for the heavy lanthanides. In complexation, all four ligands show the same trend and a high selectivity for Yb3+ (ML, log β ≥ 7). Besides the formation of ML complexes, ML2 species were also obtained. In most cases, these species were corroborated by the proton NMR studies. For partial cone-2b with Pr3+ the complexation process is enthalpically driven, whereas for 3b the formation of the ML2 species with this cation is due to a favourable entropy term. DFT studies indicate that ligand 3b forms the most stable complex with La3+, followed by partial cone-2b.