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Publicações

2004

Iransposing relations: From Maybe functions to hash tables

Autores
de Oliveira, JNF; Rodrigues, CJPC;

Publicação
MATHEMATICS OF PROGRAM CONSTRUCTION, PROCEEDINGS

Abstract
Functional transposition is a technique for converting relations into functions aimed at developing the relational algebra via the algebra of functions. This paper attempts to develop a basis for generic transposition. Two instances of this construction are considered, one applicable to any relation and the other applicable to simple relations only. Our illustration of the usefulness of the generic transpose takes advantage of the free theorem of a polymorphic function. We show how to derive laws of relational combinators as free theorems of their transposes. Finally, we relate the topic of functional transposition with the hashing technique for efficient data representation.

2004

An evolutionary algorithm for manufacturing cell formation

Autores
Goncalves, JF; Resende, MGC;

Publicação
COMPUTERS & INDUSTRIAL ENGINEERING

Abstract
Cellular manufacturing emerged as a production strategy capable of solving the certain problems of complexity and long manufacturing lead times in batch production. The fundamental problem in cellular manufacturing is the formation of product families and machine cells. This paper presents a new approach for obtaining machine cells and product families. The approach combines a local search heuristic with a genetic algorithm. Computational experience with the algorithm on a set of group technology problems available in the literature is also presented. The approach produced solutions with a grouping efficacy that is at least as good as any results previously reported in literature and improved the grouping efficacy for 59% of the problems. (C) 2004 Published by Elsevier Ltd.

2004

Optimization of OCT signal-to-noise ratio, when excess photon noise increases due to mismatch of the balanced receiver

Autores
Rosa, CC; Podoleanu, AG;

Publicação
FLUCTUATIONS AND NOISE IN PHOTONICS AND QUANTUM OPTICS II

Abstract
In optical coherence tomography (OCT), it is often assumed that the signal-to-noise ratio, at higher optical power regimes, is limited by beat noise. Nonetheless it was often noticed that the limiting value could not be experimentally achieved, despite minimizing the stray reflectance and increasing the optical source effective bandwidth. In this work we present a new model for the noise in a balanced OCT configuration, which accounts for the limited spectral response of fiber directional couplers, as well as imperfections in the photo-detectors. As a consequence, and due to different spectrum content between the two balanced-OCT outputs, excess photon noise is larger than previously considered. The model also allows for the determination of SNR optimized parameters for maximum performance of the balanced system, and can be applied to any coupler or broadband source. Results for optimized and non-optimized configurations, for different balanced detection configurations, implemented in an OCT system, are presented and discussed.

2004

Reel and sheet cutting at a paper mill

Autores
Correia, MH; Oliveira, JF; Ferreira, JS;

Publicação
COMPUTERS & OPERATIONS RESEARCH

Abstract
This work describes a real-world industrial problem of production planning and cutting optimization of reels and sheets, occurring at a Portuguese paper mill. It will focus on a particular module of the global problem, which is concerned with the determination of the width combinations of the items involved in the planning process: the main goal consists in satisfying an order set of reels and sheets that must be cut from master reels. The width combination process will determine the quantity/weight of the master reels to be produced and their cutting patterns, in order to minimize waste, while satisfying production orders. A two-phase approach has been devised, naturally dependent on the technological process involved. Details of the models and solution methods are presented. Moreover some illustrative computational results are included.

2004

Fiber Bragg grating sensing system for simultaneous measurement of salinity and temperature

Autores
Pereira, DA; Frazao, O; Santos, JL;

Publicação
OPTICAL ENGINEERING

Abstract
A fiber optic sensing system for simultaneous measurement of temperature and salinity based on fiber Bragg grating technology is presented. The fabrication process, which relies on chemical etching of the fibre, is described and its performance is evaluated. Theoretical and experimental results are given, which are summarized on the obtained resolutions of +/-0.06degreesC/ rootHz and +/- 0.2parts per thousand./ rootHz for temperature and salinity, respectively. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

2004

In situ temperature measurement of an optical fiber submitted to electric arc discharges

Autores
Rego, G; Santos, LMNBF; Schroder, B; Marques, PVS; Santos, JL; Salgado, HM;

Publicação
IEEE PHOTONICS TECHNOLOGY LETTERS

Abstract
Type S thermocouples were assembled in situ by applying high intensity electric are discharges to the contact junction of two platinum (Pt) and Pt-10% rhodium (Pt-10% Rh) wires, inserted on a silica capillary. The electrically insulated thermocouples built in this way were afterwards employed to estimate the temperature of an optical fiber subjected to arc discharges. For typical values of the arc discharge parameters used to arc-induce long-period fiber gratings (electric current I = 9 mA and arc duration t = 1 s), a capillary peak temperature value of 1420 degreesC +/- 400 degreesC was obtained by extrapolation of the experimental data for the limit situation of having a thermocouple with negligible diameter. The temperature profiles in the capillary and in an optical fiber were calculated based on a heat transfer model implemented by a finite element algorithm and fitted to the experimental temperature distribution in the Pt and Pt-10% Rh wires. The correspondent peak temperatures computed for the capillary and for the fiber were 1450 degreesC and 1320 degreesC, respectively. A good agreement between the capillary temperature values determined graphically and numerically was obtained.

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