Repositório Colecção:
http://hdl.handle.net/10198/390
2018-01-17T08:47:24ZThe use of ore microscopy data for flotation process control by means of a liberation model - a case study
http://hdl.handle.net/10198/11852
Título: The use of ore microscopy data for flotation process control by means of a liberation model - a case study
Autor: Barros, Elisa; Leite, Mário; Cavalheiro, Abílio
Resumo: Any realistic description of ore processing dealing with a particulate system requires an adequate characterization of it properties, mainly particle size and grade,because these are the most important variables that influence the performance of a mineral processing separation, such as froth flotation. Experience has shown that an appropriate model for liberation of solid phases must always integrate all available mineralogical data by comminution. The present work aims too describe a case study for calibration of a liberation model with data obtained from semi-quantitative mineralogical analysis (ore microscopy). For the specific case of random comminution, a limit probability argument is used to justify the introduction of Euler's Beta Law as well-suited tool for describing the liberantion state of a comminuted ore, because it is able to predict the grade distribution of a given iso-size fraction of such particulate system.2000-01-01T00:00:00ZExact and heuristic approaches for lot splitting and scheduling on identical parallel machines
http://hdl.handle.net/10198/11282
Título: Exact and heuristic approaches for lot splitting and scheduling on identical parallel machines
Autor: Pimentel, Carina; Alvelos, Filipe; Duarte, António J.S.T.; Carvalho, J. M.Valério de
Resumo: In this paper, we address a lot splitting and scheduling problem existent in a textile factory. The factory we study produces a set of products that are made of, or assembled from, a list of components. During production, each component can be split into one or several lots of different sizes and each lot will be produced independently on one of a group of identical parallel machines. We formulate the problem into a mixed integer programming model and develop a heuristic method to solve the model. The heuristic method is based on a network flow model with the objective to minimise the weighted sum of the total tardiness of products and the deviations occurred during production of each product. The deviation of a product is measured by the deviation of product completion time (the last component lot completion time) and completion time of the rest of components lots for the same product. We present computational results and performance measures of the network flow heuristic for a set of randomly generated instances based on real world data.2011-01-01T00:00:00ZPerformance comparison of retailing stores using a Malmquist-type index
http://hdl.handle.net/10198/10370
Título: Performance comparison of retailing stores using a Malmquist-type index
Autor: Vaz, Clara B.; Camanho, Ana S.
Resumo: This study develops a framework that combines different management science methods to provide
insights concerning the performance of retailing stores. First, the framework enables to specify
appropriate targets for stores of a retail network using data envelopment analysis. This involves
comparing stores within homogenous groups, that is, supermarkets and hypermarkets. Second, the
framework compares the overall performance of these two groups. This requires the combined use of
a Malmquist-type index and statistical tests. This index is decomposed into sub-indices for comparing
the differences between groups in terms of the efficiency spread in each group of stores and the
productivity differences between the best-practice frontiers spanned by the benchmark stores from
each group. The hypothesis tests are used to verify if the differences between groups captured by the
sub-indices are statistically significant.2012-01-01T00:00:00ZThe assessment of retailing efficiency using network data envelopment analysis
http://hdl.handle.net/10198/2785
Título: The assessment of retailing efficiency using network data envelopment analysis
Autor: Vaz, Clara B.; Camanho, Ana; Guimarães, Rui
Resumo: This paper describes a method for the assessment of retail store performance
based on Data Envelopment Analysis (DEA). The assessment considers the stores
as complex organizations that aggregate several subunits, corresponding to sections
with management autonomy. This structure motivated an analysis at two different
levels: the section level and the store level. The performance assessment of the
sections envolves a comparison among similar sections located in different stores,
and evaluates efficiency spread. This is followed by an analysis at the store level to
define targets for the sections. This analysis takes into account the interdependencies
of the sections composing a store, as they share limited resources such as the floor
area. This is achieved using a Network DEA model, which determines the maximum
store sales allowing for reallocations of area among the sections within a store. The
method developed is illustrated using a case study consisting of a Portuguese chain
of supermarkets.2010-01-01T00:00:00Z