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Publications

2013

Comparing models for lot-sizing and scheduling of single-stage continuous processes: Operations research and process systems engineering approaches

Authors
Amorim, P; Pinto Varela, T; Almada Lobo, B; Barbosa Povoa, APFD;

Publication
COMPUTERS & CHEMICAL ENGINEERING

Abstract
In the last years, several researchers from two different academic communities, the Operations Research and the Process Systems Engineering, have been developing mathematical formulations for the lot-sizing and scheduling of single-stage continuous processes with complex setup structures. This problem has been intensively studied due to its importance to a wide range of industries where a single-stage approach is suitable for production planning. This is the case of the glass container, beer, and dairy production. Recent works have been performed by both mentioned communities, however, no intense communication between these research efforts has been observed. This work attempts a systematic analysis on recent formulation developments of both communities. Based on the result of this comparison, a reformulation is proposed that outperforms in the majority of the cases the previous existent formulations for a set of systematically generated random instances.

2013

Intellectual structure of the entrepreneurship field: a tale based on three core journals

Authors
Aurora Teixeira; Elsa Ferreira;

Publication

Abstract

2013

Computational study of the covalent bonding of microcystins to cysteine residues - a reaction involved in the inhibition of the PPP family of protein phosphatases

Authors
Pereira, SR; Vasconcelos, VM; Antunes, A;

Publication
FEBS JOURNAL

Abstract
Microcystins (MCs) are cyclic peptides, produced by cyanobacteria, that are hepatotoxic to mammals. The toxicity mechanism involves the potent inhibition of protein phosphatases, as the toxins bind the catalytic subunits of five enzymes of the phosphoprotein phosphatase (PPP) family of serine/threonine-specific phosphatases: Ppp1 (aka PP1), Ppp2 (aka PP2A), Ppp4, Ppp5 and Ppp6. The interaction with the proteins includes the formation of a covalent bond with a cysteine residue. Although this reaction seems to be accessory for the inhibition of PPP enzymes, it has been suggested to play an important part in the biological role of MCs and furthermore is involved in their nonenzymatic conjugation to glutathione. In this study, the molecular interaction of microcystins with their targeted PPP catalytic subunits is reviewed, including the relevance of the covalent bond for overall inhibition. The chemical reaction that leads to the formation of the covalent bond was evaluated in silico, both thermodynamically and kinetically, using quantum mechanical-based methods. As a result, it was confirmed to be a Michael-type addition, with simultaneous abstraction of the thiol hydrogen by a water molecule, transfer of hydrogen from the water to the alpha,beta-unsaturated carbonyl group of the microcystin and addition of the sulfur to the beta-carbon of the microcystin moiety. The calculated kinetics are in agreement with previous experimental results that had indicated the reaction to occur in a second step after a fast noncovalent interaction that inhibited the enzymes per se.

2013

Coherent Noise Reduction in High Visibility Phase-Sensitive Optical Time Domain Reflectometer for Distributed Sensing of Ultrasonic Waves

Authors
Martins, HF; Martin Lopez, S; Corredera, P; Filograno, ML; Frazao, O; Gonzalez Herraez, M;

Publication
JOURNAL OF LIGHTWAVE TECHNOLOGY

Abstract
Phase-sensitive optical time domain reflectometry (phi OTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, phi OTDRs have been used mostly for the measurement of sub-kHz vibrations, normally in the context of intrusion sensing. In this paper, the authors present an experimental and theoretical description of a high-visibility phi OTDR and its performance when used for ultrasonic vibration measurements. The use of a semiconductor optical amplifier in the setup allows to suppress coherent noise and also to improve the spectral response of the pump pulses. These two advantages greatly decrease the detected intra-band noise thus allowing frequency measurements in the limits set by the time of flight of the light pulses while maintaining the simplicity of the scheme, as no post-processing, extremely high coherence lasers or coherent detection methods are required. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a fully distributed measurement of ultrasonic waves was achieved. The statistical behavior of the system was also described theoretically and characterized experimentally.

2013

Self-organized Holonic Multi-agent Manufacturing System: the Behavioural Perspective

Authors
Barbosa, J; Leitao, P; Adam, E; Trentesaux, D;

Publication
2013 IEEE INTERNATIONAL CONFERENCE ON SYSTEMS, MAN, AND CYBERNETICS (SMC 2013)

Abstract
New manufacturing control architectures rely on the decentralization of the system entities to handle in a more effective way the current constraints imposed to the highly dynamic manufacturing world. Despite of their benefits, these architectures miss the performance levels of those achieved by traditional centralized systems running without failures. This paper proposes a holonic multi-agent system architecture, based on ADACOR foundations, which considers the self-organization concept to create a two vector solution embedded in micro and macro levels. The paper describes the self-organization mechanism embed at the micro level, named behavioural self-organization, being validated using the AIP-PRIMECA flexible manufacturing system.

2013

An Adaptive Duty-Cycle Methodology for PV Power Maximization Using a Single Variable

Authors
Vidal, AA; Tavares, VG; Principe, JC;

Publication
2013 IEEE EUROCON

Abstract
This paper presents a new methodology to maximize the power output of Photovoltaic panels (PV), based on an adaptive duty-cycle methodology. The approach embeds the DC/DC converter characteristic in the cost function, allowing an optimization based on a single measured variable. Two cost functions, and respective learning rules, are derived. The first, more complex and comprehensive, traces the ground for the second which is less computational intensive and solves stability issues and implementation difficulties. It is also demonstrated that the system is asymptotically stable around the optimum duty-cycle, in the Lyapunov sense. Both methods are compared through simulations and deviations from the optimal solution are assessed.

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