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Publicações

2007

Robust vision algorithms for quadruped soccer robots

Autores
Reis, LP;

Publicação
COMPUTATIONAL MODELLING OF OBJECTS REPRESENTED IN IMAGES: FUNDAMENTALS, METHODS AND APPLICATIONS

Abstract
This paper presents a robust vision system based on semi-automatic color calibration, color segmentation and image high-level analysis for quadruped soccer playing robots. The algorithms presented were used in the context of FC Portugal legged league team that participated since 2003 in RoboCup - Robotic Soccer World Championship. Controlled experiments with variable lightning conditions are analyzed in order to conclude the robustness of our vision system.

2007

QoS abstraction layer in 4G access networks

Autores
Carneiro, G; Ricardo, M;

Publicação
TELECOMMUNICATION SYSTEMS

Abstract
Emerging access networks will use heterogeneous wireless technologies such as 802.11, 802.16 or UMTS, to offer users the best access to the Internet. Layer 2 access networks will consist of wireless bridges (access points) that isolate, concatenated, or in mesh provide access to mobile nodes. The transport of real time traffic over these networks may demand new QoS signalling, used to reserve resources. Besides the reservation, the new signalling needs to address the dynamics of the wireless links, the mobility of the terminals, and the multicast traffic. In this paper a new protocol is proposed aimed at solving this problem-the QoS Abstraction Layer (QoSAL). Existing only at the control plane, the QoSAL is located above the layer 2 and hides from layer 3 the details of each technology with respect to the QoS and to the network topology. The QoSAL has been designed, simulated, and tested. The results obtained demonstrate its usefulness in 4G networks.

2007

Fiber ring laser sensor for strain-temperature discrimination based on four-wave mixing effect

Autores
Frazao, O; Morais, R; Baptista, JM; Santos, JL;

Publicação
OPTICAL ENGINEERING

Abstract
We present a new configuration based on a fiber ring laser sensor with four-wave mixing effect generation for simultaneous measurement of strain and temperature. The fiber ring laser sensor, corresponding to the signal wavelength, is based on an erbium-doped fiber amplifier, a highly nonlinear bismuth-based optical fiber, and a Bragg grating filter. Four-wave mixing is generated when an external pump laser is combined with a ring laser sensor. Two new peaks appear and are named the converted and satellite wavelengths. With efficiency conversion, which corresponds to the optical power ratio between the converted signal and ring laser input signal, and a Bragg wavelength it is possible to discriminate strain and temperature. Maximum errors of +/- 1.8 degrees C and +/- 12 mu epsilon are reported over 100 degrees C and 1000 mu epsilon measurement ranges, respectively. (c) 2007 Society of PhotoOptical Instrumentation Engineers.

2007

HyParView: a membership protocol for reliable gossip-based broadcast

Autores
Leitao, J; Pereira, J; Rodrigues, L;

Publicação
37TH ANNUAL IEEE/IFIP INTERNATIONAL CONFERENCE ON DEPENDABLE SYSTEMS AND NETWORKS, PROCEEDINGS

Abstract
Gossip, or epidemic, protocols have emerged as a powerful strategy to implement highly scalable and resilient reliable broadcast primitives. Due to scalability reasons, each participant in a gossip protocol maintains a partial view of the system. The reliability of the gossip protocol depends upon some critical properties of these views, such as degree distribution and clustering coefficient. Several algorithms have been proposed to maintain partial views for gossip protocols. In this paper we show that tinder a high number of faults, these algorithms take a long time to restore the desirable view properties. To address this problem, we present HyParView, a new membership protocol to support gossip-based broadcast that ensures high levels of reliability even in the presence of high rates of node failure. The HyFarView protocol is based on a novel approach that relies in the use of two distinct partial views, which are maintained with different goals by different strategies.

2007

Brillouin fibre laser discrete sensor for simultaneous strain and temperature measurement

Autores
Frazao, O; Marques, JM; Santos, JL; Marques, MB; Baptista, JM;

Publicação
APPLIED PHYSICS B-LASERS AND OPTICS

Abstract
In this work, a Brillouin fibre laser sensor for strain and temperature discrimination is presented. The fibre laser sensor consists of a Fabry-Perot cavity with 20 m of optical fibre between two Bragg gratings. For the strain measurement, the 20 m were split in half and in 10 m a pre-tension was applied originating two Brillouin peaks. For the temperature measurement all of the sensing head was heated. The resolutions achieved were +/- 1 mu epsilon and +/- 1 degrees C for strain and temperature measurements, respectively.

2007

Stimulated Brillouin scattering as the referencing mechanism of an optical fibre intensity sensor

Autores
Baptista, JM; Marques, JM; Frazao, O; Santos, S; Santos, JL; Marques, MB;

Publicação
OPTICS COMMUNICATIONS

Abstract
An optical fibre intensity sensor referenced by stimulated Brillouin scattering is presented. The optical sensor uses Fresnel reflection signal at the sensor fibre end and employs an adequate relationship between Brillouin and Rayleigh scattering and Fresnel reflection to have a referenced optical fibre intensity sensor addressed in reflection.

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