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Publicações

2013

Biomechanical Modeling and Simulation of the Spider Crab (Maja brachydactyla)

Autores
Rynkevic, R; Silva, MF; Marques, MA;

Publicação
2013 IEEE 3RD PORTUGUESE MEETING IN BIOENGINEERING (ENBENG)

Abstract
One line of research and development in robotics receiving increasing attention in recent years is the development of biologically inspired walking robots. The purpose is to gain knowledge of biological beings and apply that knowledge to implement the same methods of locomotion ( or at least use the biological inspiration) on the machines we build. It is believed that this way it is possible to develop machines with capabilities similar to those of biological beings in terms of locomotion skills and energy efficiency. One way to better understand the functioning of these systems, without the need to develop prototypes with long and costly development, is to use simulation models. Based on these ideas, this work concerns the biomechanical study of the spider crab, using the SimMechanics toolbox of Matlab/Simulink. This paper describes the anatomy and locomotion of the spider crab, its modeling and control and the locomotion simulation of a crab within the SimMechanics environment.

2013

Delay-aware DWT-based image transmission in wireless visual sensor networks

Autores
Costa, DG; Guedes, LA; Vasques, F; Portugal, P;

Publicação
WebMedia 2013 - Proceedings of the 19th Brazilian Symposium on Multimedia and the Web

Abstract
Wireless sensor networks have been employed as an effective tool for a large set of monitoring applications, directly supporting applications not addressed by conventional Internet-based technologies. Camera-enabled sensors enhance the applicability of those networks allowing innovative visual monitoring functions. Sometimes, source nodes will perform real-time monitoring of an area of interest, where visual data packets will need to be transmitted with minimum delay. However, energy depletion of the nodes that compose the transmission paths may hamper the network capability to deliver packets with time constraints. In such context, we propose a delay-aware image transmission mechanism where the relevancies of DWT subbands are considered when forwarding packets to the next hop toward the sink. In fact, parts of DWT-based encoded visual data may have different relevancies for the reconstruction of the original visual information and those relevancies may be exploited when forwarding packets. In the proposed approach, high-relevant packets are forwarded through paths with lower average end-to-end delay, while the remaining packets flow through paths high higher delay, allowing that low-quality versions of the transmitted images reach the sink as soon as possible. Moreover, the best paths will need to relay fewer packets, potentially reducing energy consumption and enlarging their lifetime. We present simulation results to attest the benefits of the proposed mechanism. © 2013 ACM.

2013

Simplified back-propagation for fibre nonlinearity compensation employing multi-band OFDM signals

Autores
Pessoa, LM; Salgado, HM; Darwazeh, I;

Publicação
OPTICAL AND QUANTUM ELECTRONICS

Abstract
In this paper we investigate the efficacy of applying the coupled field back-propagation algorithm as a post-compensation method for nonlinearity mitigation in a coherently detected fibre optic long-haul system using multi-band orthogonal frequency division multiplexed signals. Specifically, we analyze the impact of varying the band-spacing and the number of bands. We find that its efficacy is higher for largely spaced bands and a small number of bands. Additionally, we propose a method to include the Four Wave Mixing compensating term within the coupled field method to provide simplified means of multichannel compensation. We conclude that this method is more efficient in improving the performance especially for small band spacings. The coupled field method proves to be an interesting choice for the implementation of receiver-based real-time digital signal processing.

2013

Customer attrition in retailing: An application of Multivariate Adaptive Regression Splines

Autores
Migueis, VL; Camanho, A; Falcao e Cunha, JFE;

Publicação
EXPERT SYSTEMS WITH APPLICATIONS

Abstract
The profit resulting from customer relationship is essential to ensure companies viability, so an improvement in customer retention is crucial for competitiveness. As such, companies have recognized the importance of customer centered strategies and consequently customer relationship management (CRM) is often at the core of their strategic plans. In this context, a priori knowledge about the risk of a given customer to mitigate or even end the relationship with the provider is valuable information that allows companies to take preventive measures to avoid defection. This paper proposes a model to predict partial defection, using two classification techniques: Logistic regression and Multivariate Adaptive Regression Splines (MARS). The main objective is to compare the performance of MARS with Logistic regression in modeling customer attrition. This paper considers the general form of Logistic regression and Logistic regression combined with a wrapper feature selection approach, such as stepwise approach. The empirical results showed that MARS performs better than Logistic regression when variable selection procedures are not used. However, MARS loses its superiority when Logistic regression is conducted with stepwise feature selection.

2013

Dynamic Supply Chains: Models, Organizational Issues and Supporting Technologies

Autores
Bastos, João; Azevedo, Américo; Ávila, Paulo;

Publicação
4th Industrial Engineering and Management Symposium

Abstract
In recent decades, with globalization, the financial crisis and the entry of new players in the global markets, the industrial enterprises in order to survive are forced to update its supply chain strategy in line with the new and challenging circumstances. Thus, company managers have put a growing interest in developing strategies designed to provide companies with the resources, capabilities and ICT technologies in order to compete successfully in the market. Supply chain managers increasingly understand that it is the time to fundamentally rethink how to design and operate the supply chains that link with their own company, namely suppliers and customers. For too long, there has been a major concern with infrastructures, resource utilization and cut costing in the operation activities, ultimately in efficiency. However, even recognizing that maintaining lower levels of operating costs are important, achieving and maintaining future competitiveness demands more sophistication.

2013

Wave-front reconstruction for the non-linear curvature wave-front sensor

Autores
Correia, C; Veran, JP; Guyon, O; Clergeon, C;

Publicação
3rd AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes

Abstract
Non-linear curvature wave-front sensing (nlCWFS) delivers outstanding sensitivity and high dynamic range by lifting the linearity constraint of standard curvature wave-front sensing and working in the non-linear Fresnel (near-field) regime [Guyon, 2010]. The goals of this paper are twofold: 1) revisit the phase-diversity PD formalism and attempt to use this framework, originally developed for the Fraunhofer (far-field) regime, with nlCWFS signals and 2) develop formulae making explicit use of the Fresnel regime for later use with gradient-based non-linear minimisation methods.

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