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Publicações

Publicações por LIAAD

2001

Explosion of smoothness from a point to everywhere for conjugacies between Markov families

Autores
Ferreira, F; Pinto, AA;

Publicação
DYNAMICAL SYSTEMS-AN INTERNATIONAL JOURNAL

Abstract
For uniformly asymptotically affine (uaa) Markov maps on train tracks, we prove the following type of rigidity result: if a topological conjugacy between them is (uaa) at a point in the train track then the conjugacy is (uaa) everywhere. In particular, our methods apply to the case in which the domains of the Markov maps are Canter sets. We also present similar statements for (uaa:) and C-r Markov families. These results generalize the similar ones of Sullivan and de Faria for C-r expanding circle maps with r > 1 and have useful applications to hyperbolic dynamics on surfaces and laminations.

2001

Existence, uniqueness and ratio decomposition for Gibbs states via duality

Autores
Pinto, AA; Rand, DA;

Publicação
ERGODIC THEORY AND DYNAMICAL SYSTEMS

Abstract
We give an elementary proof of existence and uniqueness of Gibbs states for Holder weight systems on subshifts of finite type. This uses a notion of duality for such subshifts. The approach of Paterson [2] is used to construct a measure with a prescribed Jacobian and the duality is used to produce an invariant measure from this.

2001

Effect of temperature on evolution of free amino acid and biogenic amine contents during storage of Azeitao cheese

Autores
Pinho, O; Ferreira, IMPLVO; Mendes, E; Oliveira, BM; Ferreira, M;

Publicação
FOOD CHEMISTRY

Abstract
A study on the evolution of free amino acids and biogenic amines in Azeitao cheese during 4 weeks at different temperatures of storage (4 and 25 degreesC) was performed. Free amino acids and biogenic amines were determined by RP-HPLC with visible detection, following extraction from the cheese and derivatization with dabsyl chloride. The method presented a linear relation between peak area and concentration from 2-200 mg/l. The detection limit value was less than 1.5 mg/l. The average repeatability was less than 4%. The major free amino acids were proline, valine, isoleucine and leucine and the major amines were tyramine, cadaverine and histamine. Room temperature (25 degreesC) promoted a significant increase of the contents of valine, leucine, tyramine and putrescine, expressed as g/kg of dry matter. These two free amino acids and two biogenic amines may serve as indicators of temperatures changes in ripened cheese.

2001

On-line subspace identification

Autores
Delgado, CJM; dos Santos, PL; de Carvalho, JLM;

Publicação
6th European Control Conference, ECC 2001, Porto, Portugal, September 4-7, 2001

Abstract
In this paper a recursive technique, based on the subspace state space identification methods, is presented for identification of time-varying systems. The main idea was to develop an iterative algorithm with most of the advantages of this kind of methods in order to deal with real-time applications and minimize the computational burden. As a subspace-based state space system identification technique, it has two main steps: first, a state vector sequence is estimated, using numerical linear algebra tools, then the state space model is obtained from a simple least squares model. © 2001 EUCA.

2001

A parallel algorithm for the simulation of the dynamic behaviour of liquid-liquid agitated columns

Autores
Gomes, EF; Ribeiro, LM; Regueiras, PFR; Cruz Pinto, JJC;

Publicação
VECTOR AND PARALLEL PROCESSING - VECPAR 2000

Abstract
Simulation of the dynamic behaviour of liquid-liquid systems is of prominent importance in many industrial fields. Algorithms for fast and reliable simulation of single stirred vessels and extraction columns have already been published by some of the present authors. In this work, we propose a methodology to develop a parallel version of a previously validated sequential algorithm, for the simulation of a liquid-liquid Kuhni column. We also discuss the algorithm implementation in a distributed memory parallel-computing environment, using MPI. Despite the difficulties encountered to preserve efficiency in the case of a heterogeneous cluster, the results demonstrate performance improvements that clearly indicate that the approach followed may be successfully extended to allow real-time plant control applications.

2000

Integrating rules and cases in learning via case explanation and paradigm shift

Autores
Lopes, AD; Jorge, A;

Publicação
ADVANCES IN ARTIFICIAL INTELLIGENCE

Abstract
In this article we discuss in detail two techniques for rule and case integration. Case-based learning is used when the rule language is exhausted. Initially, all the examples are used to induce a set of rules with satisfactory quality. The examples that are not covered by these rules are then handled as cases. The case-based approach used also combines rules and cases internally. Instead of only storing the cases as provided, it has a learning phase where, for each case, it constructs and stores a set of explanations with support and confidence above given thresholds. These explanations have different levels of generality and the maximally specific one corresponds to the case itself. The same case may have different explanations representing different perspectives of the case. Therefore, to classify a new case, it looks for relevant stored explanations applicable to the new case. The different possible views of the case given by the explanations correspond to considering different sets of conditions/features to analyze the case. In other words, they lead to different ways to compute similarity between known cases/explanations and the new case to be classified (as opposed to the commonly used fixed metric).

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