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Publications

2000

The effects of temporal aggregation on tests of linearity of a time series

Authors
Teles, P; Wei, WWS;

Publication
COMPUTATIONAL STATISTICS & DATA ANALYSIS

Abstract
Time-series aggregates are often used in performing tests for departure from linearity. In this paper, we study the effects of temporal aggregation on testing for linearity, basing our analysis on both time- and frequency-domain tests. The results show that temporal aggregation weakens nonlinearity and reduces the power of the tests. The impact is severe. The use of aggregate data greatly hampers the detection of the nonlinear nature of the process.

2000

Analysis of the flyback effects on the serrodyne interferometric demodulation of fiber optic Bragg grating sensors

Authors
Jorge, PAS; Ferreira, LA; Santos, JL;

Publication
OPTICAL ENGINEERING

Abstract
An analysis is performed of the degradation of the signal readout of fiber optic Bragg grating sensors demodulated using the serrodyne interferometric technique. Experimental results are presented that validate the analysis. It is also shown that synchronous detection of the interferometric signal referenced to the serrodyne waveform that modulates the phase of the readout interferometer allows the elimination of the system do offset introduced by the serrodyne flyback, (C) 2000 Society of Photo-Optical Instrumentation Engineers.

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

Computational depth

Authors
Antunes, L; Fortnow, L; van Melkebeek, D;

Publication
16TH ANNUAL IEEE CONFERENCE ON COMPUTATIONAL COMPLEXITY, PROCEEDINGS

Abstract
We introduce Computational Depth, a measure for the amount of "nonrandom" or "useful" information in a string by considering the difference of various Kolmogorov complexity measures. We investigate three instantiations of Computational Depth: Basic Computational Depth, a clean notion capturing the spirit of Bennett's Logical Depth. Time-t Computational Depth and the resulting concept of Shallow Sets, a generalization of sparse and random sets based on low depth properties of their characteristic sequences. We show that every, computable set that is reducible to a shallow set has polynomial-size circuits. Distinguishing Computational Depth, measuring when strings are easier to recognize than to produce. We show that if a Boolean formula has a nonnegligible fraction of its satisfying assignments with low depth, then we can find a satisfying assignment efficiently.

2000

Power system state estimation - An overview

Authors
Ferreira, IM; Carvalho, JB; Barbosa, FM;

Publication
Proceedings of the Universities Power Engineering Conference

Abstract
Today, the State Estimation is considered as the heart of nearly all modern network control centers. Among other factors, the technical developments in fast data communication network technology opens up the possibility of parallel and distributed implementations of the state estimation function. This paper provides an overview of the state of the art in Power Systems State Estimation.

2000

A component-based approach to support order planning in a distributed manufacturing enterprise

Authors
Azevedo, AL; Sousa, JP;

Publication
JOURNAL OF MATERIALS PROCESSING TECHNOLOGY

Abstract
Traditional Production Planning and Control systems do not successfully deal with new organisational forms of manufacturing, like production "islands", product oriented or customer driven production. These current trends lead in practice to a strong decentralisation of production management tasks and to an "object oriented structuring" of the manufacturing process. Planning and operation in this global environment requires new skills and new approaches, namely, the co-ordination of global networks of manufacturing units and of large complex supply chains. In this paper, we present a decentralised information system designed to address the tasks of production planning that result from sales orders, originated in customers located anywhere in the world, and accomplished through a distributed manufacturing network. The system addresses the requirements of a make-to-order environment and is hopefully able to produce realistic satisfactory delivery dates. The information infrastructure designed and implemented using distributed object-oriented technology with a component based architecture has proven to be efficient and powerful, satisfying all the major tight requirements of information systems in an environment of distributed manufacturing.

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