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Publicações

2009

IMPROVING THE JOB-SHOP WORKLOAD CONTROL THROUGH ORDER ACCEPTANCE AND DUE-DATE NEGOTIATION

Autores
Alves Moreira, MDA;

Publicação
EUROPEAN SIMULATION AND MODELLING CONFERENCE 2009

Abstract
Work flows in a job-shop are determined not only by the release load but also by the number of accepted orders. In this paper the common assumption of accepting all incoming orders regardless of shop condition is relaxed. Instead of placing the orders in a 'pre-shop pool' queue, as in previous research, orders that arrive at the shop, when it is highly congested, may be immediately rejected or their due dates may be negotiated. This paper explores the idea of controlling the workload since the acceptance/rejection stage. A new acceptance/rejection rule is proposed, and tests are conducted to study the sensitivity of job-shop performance to different order acceptance parameters, like the tolerance of the workload limit and the due date extension acceptance. The effect of the negotiation phase on the job-shop performance is evaluated using a simulation model of a generic random job-shop that allow us to conclude that having a negotiation phase prior to rejection improves almost all workload performance measures. Different tolerances of the workload limit slightly affect the performance of the job-shop.

2009

A nonlinear mobile robot modeling applied to a model predictive controller

Autores
Conceicao, AS; Moreira, AP; Costa, P;

Publicação
Proceedings of the ACM Symposium on Applied Computing

Abstract
This paper presents a nonlinear modeling approach of an omnidirectional mobile robot to predict the robot behavior in a model-based predictive controller (MPC). Parameters related to dynamic equations of the robot and restriction of the robot's motors are considered in the modeling. Simulation results and real results of navigation are provided to demonstrate the performance of the proposed modeling approach. Copyright 2009 ACM.

2009

Coordinated voltage support in distribution networks with distributed generation and microgrids

Autores
Madureira, AG; Pecas Lopes, JAP;

Publicação
IET RENEWABLE POWER GENERATION

Abstract
This paper proposes a new methodology for coordinated voltage support in distribution networks with large integration of distributed generation and microgrids. Given the characteristics of the LV networks, it is shown that traditional control strategies using only reactive power control may not be sufficient in order to perform efficient voltage control. Therefore, microgeneration shedding must also be employed, especially in scenarios with extreme microgeneration penetration. An optimisation tool based on a meta-heuristic approach was developed to address the voltage control problem. In addition, neural networks were employed in order to decrease computational time, thus enabling the use of the tool for online operation. The results obtained revealed good performance of this control approach.

2009

Rapid thermal annealing and conventional furnace effect on SrBi2Ta2O9 thin films crystallization

Autores
Gonzalez Aguilar, G; Salvado, IMM; Costa, ME;

Publicação
THIN SOLID FILMS

Abstract
The effect of rapid thermal annealing and conventional furnace annealing on the crystallization of SrBi2Ta2O9 is modeled using an Arrhenius-type equation. Based on previous experimental results several authors have suspected that different reaction mechanisms occur depending of the heating rate employed in these two treatment methods. Oppositely, the results here presented and the analysis of reported data suggest two concurrent reaction mechanisms 1) direct transformation of the reagents into the perovskite phase and 2) transformation of an intermediate into the perovskite phase. Another important conclusion here obtained confirms the validity of the Arrhenius equation to predict the behavior of the crystallization process by either of the two heating methods mentioned above.

2009

Architecture of an innovative system for the acquisition of products in supermarkets - Business model [Arquitectura para um sistema inovador de aquisição de produtos em grandes superfícies-Modelo de negócio]

Autores
Santos, D; Pereira, A; Goncalves, R;

Publicação
Actas da 4a Conferencia Iberica de Sistemas e Tecnologias de Informacao, CISTI 2009

Abstract

2009

mtDNA GeneExtractor: A computer tool for mtDNA gene/region information extraction

Autores
Freitas, F; Oliveira, S; Rocha, R; Pereira, L;

Publicação
MITOCHONDRION

Abstract
The analysis of considerable numbers of DNA sequences is largely dependent on the development of simple software tools for automatically process the genetic data deposited on public databases. However, there are some difficulties in the automation process due to diverse synonyms being used as qualifiers for genes and some inconsistencies in gene locations between related Primate species, this fact happening even in the carefully curated database RefSeq. Here, we present mtDNA GeneEXtractor, a Windows based computer tool developed for the extraction of information for particular gene/regions from mammal mitochondrial DNA sequences deposited under GenBank format. The tool was quite efficient in retrieving organized information for comparative mtDNA gene/region diversity analyses when tested for the evaluation of transition/transversion ratios in humans and between Primates. Taking phylogenetic information into account to avoid redundancy due to ancestry-sharing, the transition/transversion ratios in the 13 protein-coding genes had a mean value of 12.46 for Primates (from 6.46 in ND2 to 17.04 in COX1) and higher (34.74) but more heterogeneous (ranging from 17.30 in ND5 to 74.39 in ND4) in a worldwide human database. The similar patterns of transition/transversion ratios in all positions and in only four fold degenerate positions show no evidence for selection in the 13 mtDNA protein-coding genes.

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