2009
Autores
Marques, V; Farinha, JT; Brito, A;
Publicação
PROCEEDINGS OF THE 13TH WSEAS INTERNATIONAL CONFERENCE ON COMPUTERS
Abstract
This paper is divided into three parts: the first one introduces SADEX, a fuzzy Case Based Reasoning (CBR) Expert System (ES) for fault diagnosis. The second focus on its observation relevance factors and shows how the results are in entire agreement with the relevance concept introduced by Robertson and Spark-Jones in their well known and proved technique of document retrieval. Finally we describe how the equipment composition information can be used to generalize and adapt case solutions to unknown occurrences. This generalization is based on a taxonomic similarity between functionally autonomous modules (FAM) or components. Some formulae for evaluating this similarity are derived.
2009
Autores
Lopes, IS; Leitao, AF; Pereira, GAB;
Publicação
SAFETY, RELIABILITY AND RISK ANALYSIS: THEORY, METHODS AND APPLICATIONS, VOLS 1-4
Abstract
In industry, spare equipments are often shared by many workplaces with identical equipments to assure the production rate required to fulfill delivery dates. These types of systems arc called "Maintenance Float Systems". The main objective of managers that deal with these types of systems is to assure the required capacity to deliver orders on time and at minimum cost. Not delivering on time has often important consequences; it call cause loss of costumer goodwill, loss of sales and call damage organization's image. Maintenance cost is the indicator more frequently used to configure maintenance float systems and to invest in maintenance workers or spare equipments. Once the system is configured, other performance indicators must be used to characterize and measure the efficiency of the system. Different improvement initiatives call be performed to enhance the performance of maintenance float systems: performing preventive maintenance actions, implementation of autonomous maintenance, improvement of equipments maintainability, increase of maintenance crews' efficiency etc. "Carrying out improvement based on facts" is a principle of Total Quality Management (TQM) in order to step to business excellence. It requires monitoring processes through performance measures. This work aims to characterize and highlight the differences and relationships between three types of performance measures-equipment availability, equipment utilization and workplace occupation, in the context of maintenance float system. Definitions and expressions of these three indicators are developed for maintenance float systems. The relationship between maintenance float systems efficiency and the referred indicators is shown. Other indicators are also proposed and compared with the first ones (number of standby equipments, queue length etc.).
2009
Autores
Nobre, C; Santos, MJ; Dominguez, A; Torres, D; Rocha, O; Peres, AM; Rocha, I; Ferreira, EC; Teixeira, JA; Rodrigues, LR;
Publicação
ANALYTICA CHIMICA ACTA
Abstract
Adsorption equilibrium of fructose, glucose and sucrose was evaluated on sulfonated poly(styrene-co-divinylbenzene) cation-exchange resins. Two types of resins were used: potassium (K(+)) gel-type and sodium (Na(+)) macroporous resins. Influence of the cation and effect of the resin structure on adsorption were studied. The adsorption isotherms were determined by the static method in batch mode for mono-component and multi-component sugar mixtures, at 25 and 40 degrees C, in a range of concentrations between 5 and 250gL(-1). All adsorption isotherms were fitted by a linear model in this range of concentrations. Sugars were adsorbed in both resins by the following order: fructose > glucose > sucrose. Sucrose was more adsorbed in the Na(+) macroporous resin, glucose was identically adsorbed, and fructose was more adsorbed in the K(+) gel-type resin. Data obtained from the adsorption of multi-component mixtures as compared to the mono-component ones showed a competitive effect on the adsorption at 25 degrees C, and a synergetic effect at 40 degrees C. The temperature increase conducted to a decrease on the adsorption capacity for mono-component Sugar mixtures, and to an increase for the multi-component mixtures. Based on the selectivity results, K(+) gel-type resin seems to be the best choice for the separation of fructose, glucose and sucrose, at 25 degrees C.
2009
Autores
Alvelos, F; Chan, TM; Vilaca, P; Gomes, T; Silva, E; Valerio de Carvalho, JMV;
Publicação
ENGINEERING OPTIMIZATION
Abstract
This article addresses several variants of the two-dimensional bin packing problem. In the most basic version of the problem it is intended to pack a given number of rectangular items with given sizes in rectangular bins in such a way that the number of bins used is minimized. Different heuristic approaches (greedy, local search, and variable neighbourhood descent) are proposed for solving four guillotine two-dimensional bin packing problems. The heuristics are based on the definition of a packing sequence for items and in a set of criteria for packing one item in a current partial solution. Several extensions are introduced to deal with issues pointed out by two furniture companies. Extensive computational results on instances from the literature and from the two furniture companies are reported and compared with optimal solutions, solutions from other five (meta) heuristics and, for a small set of instances, with the ones used in the companies.
2008
Autores
Parreno, F; Alvarez Valdes, R; Tamarit, JM; Oliveira, JF;
Publicação
INFORMS JOURNAL ON COMPUTING
Abstract
In this paper, a greedy randomized adaptive search procedure (GRASP) for the container loading problem is presented. This approach is based on a constructive block heuristic that builds upon the concept of maximal space, a nondisjoint representation of the free space in a container. This new algorithm is extensively tested over the complete set of Bischoff and Ratcliff problems [Bischoff, E. E., M. S. W. Ratcliff. 1995. Issues in the development of approaches to container loading. Omega 23 377-390], ranging from weakly heterogeneous to strongly heterogeneous cargo, and outperforms all the known nonparallel approaches that, partially or completely, have used this set of test problems. When comparing against parallel algorithms, it is better on average but not for every class of problem. In terms of efficiency, this approach runs in much less computing time than that required by parallel methods. Thorough computational experiments concerning the evaluation of the impact of algorithm design choices and internal parameters on the overall efficiency of this new approach are also presented.
2008
Autores
Almada Lobo, B; Oliveira, JF; Carravilla, MA;
Publicação
COMPUTERS & OPERATIONS RESEARCH
Abstract
Gupta and Magnusson [The capacitated lot-sizing and scheduling problem with sequence-dependent setup costs and setup times. Computers and Operations Research 2005;32(4):727-47] develop a model for the single machine capacitated lot-sizing and scheduling problem (CLSP) with sequence dependent setup times and setup costs, incorporating all the usual features of setup carryovers. In this note we show that this model does not avoid disconnected subtours. A new set of constraints is added to the model to provide an exact formulation for this problem.
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