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Publications

Publications by CRAS

2000

5dpo team description

Authors
Costa, P; Moreira, A; Sousa, A; Marques, P; Costa, P; Matos, A;

Publication
ROBOCUP-99: ROBOT SOCCER WORLD CUP III

Abstract
This paper describes the 5dpo team. The paper will be divided into three main sections, corresponding to three main blocks: the Global Level, the Local Level and the Interface Level. These Levels, their subsystems and some implementation details will be described next.

2000

5dpo-2000 team description

Authors
Costa, P; Moreira, A; Sousa, A; Marques, P; Costa, P; Matos, A;

Publication
ROBOCUP-99: ROBOT SOCCER WORLD CUP III

Abstract
This paper describes the 5dpo-2000 team, The paper will be divided into three main sections, corresponding to three main blocks: the Global Level, the Local Level and the Interface Level. These Levels, their subsystems and some implementation details will be described next.

2000

Solving conflicting beliefs with a distributed belief revision approach

Authors
Malheiro, B; Oliveira, E;

Publication
ADVANCES IN ARTIFICIAL INTELLIGENCE

Abstract
The ability to solve conflicting beliefs is crucial for multiagent systems where the information is dynamic, incomplete and distributed over a group of autonomous agents. The proposed distributed belief revision approach consists of a distributed truth maintenance system and a set of autonomous belief revision methodologies. The agents have partial views and, frequently, hold disparate beliefs which are automatically detected by system's reason maintenance mechanism. The nature of these conflicts is dynamic and requires adequate methodologies for conflict resolution. The two types of conflicting beliefs addressed in this paper are Context Dependent and Context Independent Conflicts which result, in the first case, from the assignment, by different agents, of opposite belief statuses to the same belief, and, in the latter case, from holding contradictory distinct beliefs. The belief revision methodology for solving Context Independent Conflicts is, basically, a selection process based on the assessment of the credibility of the opposing belief statuses. The belief revision methodology for solving Context Dependent Conflicts is, essentially, a search process for a consensual alternative based on a "next best" relaxation strategy.

2000

Data driven underwater transient detection based on time-frequency distributions

Authors
Oliveira, PM; Barroso, V;

Publication
OCEANS 2000 MTS/IEEE - WHERE MARINE SCIENCE AND TECHNOLOGY MEET, VOLS 1-3, CONFERENCE PROCEEDINGS

Abstract
The complexity of real-life transients, coupled with the incomplete (or absent) knowledge of their statistical structure or defining features has motivated the interest on the use of blind, data driven detection schemes. One such scheme, proposed by Jones and Sayeed, uses Time-Frequency distributions to implement sub-optimal quadratic detectors which, under certain conditions, approach the performance of optimal quadratic detectors. However, their use of Fisher's discriminants to obtain class separation has some drawbacks, which we solve by using a simple perceptron to obtain the discriminant. Also, more often than not, we will have a multiclass situation, implying the use of different Time-Frequency Distributions, each one of them tuned for a given class of transients. The different nature of these distributions (bias, type of cross-terms, time-frequency resolution, etc.) will hamper the performance of the algorithm, forcing the need for experimental validation of its heuristical aspects. These are the issues we will address. The algorithm will be applied to real data, and its performance investigated.

2000

Uncertainty in the time-frequency plane

Authors
Oliveira, PM; Barroso, V;

Publication
PROCEEDINGS OF THE TENTH IEEE WORKSHOP ON STATISTICAL SIGNAL AND ARRAY PROCESSING

Abstract
Is there a limit to the maximum resolution one can achieve when representing the signal's energy in the Time-Frequency plane? Some authors sustain that such a limit exists, and ignoring it is the cause of the known difficulties with some joint Time-Frequency distributions; others maintain that there is no such limit. In this article, we propose to analyze the merits and demerits of the several existing approaches, and suggest further arguments one might wish to consider. This will take us to the conclusion that, both from a tool-specific and from a general information-theoretic point of view, there is, indeed, a lower limit on the achievable resolution, even though the expression for that limit can not be given by the traditional Heisenberg-Gabor relations.

2000

Definitions of Instantaneous Frequency under physical constraints

Authors
Oliveira, PM; Barroso, V;

Publication
JOURNAL OF THE FRANKLIN INSTITUTE-ENGINEERING AND APPLIED MATHEMATICS

Abstract
Ville's definition of Instantaneous Frequency (IF), even though widely used and accepted, fails in most cases of practical interest. This failure has been often reported, namely in the multicomponent case. In this paper, we will analyze the advantages and shortcomings of that definition, and determine when and why it fails, integrating all previously reported cases of failure in a simple unified theory. We will also be able to extrapolate and predict the behavior of the traditional definition for any type of multicomponent signal. Alternative definitions of IF are discussed.

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