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Publications

2001

Application of highly nondegenerate cascaded four-wave mixing to high order harmonic generation

Authors
Crespo, H; Mendonca, JT; Guerreiro, A;

Publication
ECLIM 2000: 26TH EUROPEAN CONFERENCE ON LASER INTERACTION WITH MATTER

Abstract
We propose to use nondegenerate cascaded four-wave mixing processes for efficient high order harmonic generation in plasmas and dielectrics. A simple model is used to estimate the temporal duration and maximum order of the generated harmonics for both a typical laser-produced plasma and a glass slide. In the plasma case, we expect considerable pulse compression, with the production of sub-femtosecond pulses starting from the 8th harmonic.

2001

A multi-agent based cell controller

Authors
Leitao, P; Restivo, F; Putnik, G;

Publication
ETFA 2001: 8TH IEEE INTERNATIONAL CONFERENCE ON EMERGING TECHNOLOGIES AND FACTORY AUTOMATION, VOL 2, PROCEEDINGS

Abstract
This paper discusses the opportunity to use multi-agents technology in automation and distributed manufacturing systems and the expected improvements. To support the discussion, it is described a manufacturing cell control application developed using the multi-agent technology, and the results are compared with other control application developed in the past by some of the authors, using a traditional approach, for the same flexible manufacturing cell.

2001

Segmentation of object motion: matching psychophysics and computational models

Authors
Santos, JA; Campilho, A; Baptista, C; Correia, MV; Noriega, P; Albuquerque, PB;

Publication
PERCEPTION

Abstract

2001

A new method for high-harmonic generation by cascaded four-wave mixing

Authors
Mendonca, JT; Crespo, H; Guerreiro, A;

Publication
OPTICS COMMUNICATIONS

Abstract
A new method of high-harmonic generation by intense and short laser pulses is proposed. This method is based on the idea that, in quite general situations, a cascade of four-wave-mixing processes can occur. A theoretical model is established and exact analytic solutions are obtained. Examples of possible experiments in low-charged plasmas and in glass are discussed in detail, including the phase-matching conditions, the angular spread of the secondary beams and the pulse durations. Numerical examples of the possible generation of sub-femtosecond pulses are also given.

2001

The DEAR-COTS replication framework

Authors
Pinho, LM; Vasques, F; Wellings, A;

Publication
13TH EUROMICRO CONFERENCE ON REAL-TIME SYSTEMS, PROCEEDINGS

Abstract
The DEAR-COTS (Distributed Embedded ARchitecture using Commercial Off-The-Shelf components) architecture provides a COTS-based framework to execute reliable hard real-time applications. To ease the task of building reliable real-time applications on top of COTS components, a simple and transparent programming model is provided, in order that programmers abstract from the low-level implementation details of distribution and replication issues, These issues are only dealt with in a later configuration phase, where the system is configured and distributed over the DEAR-COTS nodes. This paper presents the proposed programming framework, and demonstrates how it can be used to support the transparent replication of software components.

2001

Evaluating the duration of message transactions in broadcast wired/wireless fieldbus networks

Authors
Alves, M; Tovar, E; Vasques, F;

Publication
IECON'01: 27TH ANNUAL CONFERENCE OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY, VOLS 1-3

Abstract
Determining the response time of message transactions is one of the major concerns in the design of any distributed computer-controlled system. Such response time is mainly dependent on the medium access delay, the message length and the transmission delay. While the medium access delay in fieldbus networks has been thoroughly studied in the last few years, the transmission delay has been almost ignored as it is considered that it can be neglected when compared to the length of the message itself. Nevertheless, this assumption is no longer valid when considering the case of hybrid wired/wireless fieldbus networks, where the transmission delay through a series of different mediums can be several orders of magnitude longer than the length of the message itself. In this paper, we show how to compute the duration of message transactions in hybrid wired/wireless fieldbus networks. This duration is mainly dependent on the duration of the request and response frames and on the number and type of physical mediums that the frames must cross between initiator and responder. A case study of a hybrid wired/wireless fieldbus network is also presented, where it becomes clear the interest of the proposed approach.

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