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Publicações

2008

A meta-heuristic approach to the unit commitment problem under network constraints

Autores
Pereira, J; Viana, A; Lucus, BG; Matos, M;

Publicação
International Journal of Energy Sector Management

Abstract
Purpose - The purpose of this paper is to solve the problem of committing electric power generators (unit commitment, UC), considering network constraints. Design/methodology/approach - The UC is first solved with a local search based meta-heuristic, following the assumption that all generators and loads are connected to a single network node. For evaluation purposes, the economical production levels of the units committed are computed by running a pre-dispatch algorithm where network constraints are not included. If a good quality solution is reached, an economic dispatch (ED) with network constraints is performed, where the geographic location of generators and loads are considered. Therefore, the production level of each committed generator is performed that leads to the global lowest solution cost, regarding both the generators' costs and constraints and the power system network constraints. Findings - The algorithm proposed is computationally efficient, given the time available for decision making. In addition, the solution for this algorithm, in terms of minimization of total costs, is generally better than the solution of the two phases approach. Some contractual and legal aspects related with the injection in network connections can also be included in the model. Practical implications - UC with network constraints has a large potential of use, especially for small and medium size power systems. It reflects reality in a closer way and provides a more complete and realistic knowledge about the system in operation. Originality/value - The paper presents an approach where theED with network constraints is integrated with the UC procedure. The model described is currently implemented in an EMS package offered in the market - making it a case of successful transfer from science to industry.

2008

Do cultivar, geographical location and crop season influence phenolic profile of walnut leaves?

Autores
Amaral, JS; Valentao, P; Andrade, PB; Martins, RC; Seabra, RM;

Publicação
MOLECULES

Abstract
Walnut leaves from nine different cultivars (Arco, Franquette, Hartley, Lara, Marbot, Mayette, Meylannaise, Parisienne and Rego) were studied for their phenolic compounds. Samples were harvested along three consecutive years, at two different geographical locations, in order to evaluate if significant differences in the phenolics composition can be related with genetic, climatic or geographical factors. Nine compounds (3-caffeoylquinic, 3-p-coumaroylquinic and 4-p-coumaroylquinic acids, quercetin 3-galactoside, quercetin 3-arabinoside, quercetin 3-xyloside, quercetin 3-rhamnoside, a quercetin 3-pentoside derivative and a kaempferol 3-pentoside derivative) were quantified using an HPLC-DAD methodology. The qualitative profiles were identical for all samples, but differences were observed in terms of individual compounds' contents. Multivariate statistical analysis was carried out, showing that significant differences exist among production years, which can be related to climatic reasons.

2008

Ontology Development in Collaborative Networks as a Process of Social Construction of Meaning

Autores
Pereira, C; Soares, AL;

Publicação
ON THE MOVE TO MEANINGFUL INTERNET SYSTEMS: OTM 2008 WORKSHOPS

Abstract
This paper proposes a new method to support the collaborative construction of semantic artifacts in an inter-organizational context. It aims at being applied, in particular, in the early phases of ontology development. We share the view that that the development of semantic artifacts in collaborative networks of organizations should be based on a continuous construction of meaning, rather than pursuing the delivery of highly formalized accounts of domains. For that, our research is directed to the application of cognitive semantics results, specifically by developing and extending the Conceptual Blending Theory to cope with the socio-cognitive aspects of inter-organizational ontology development. Besides the Outline of the method, we analyze the main problems and gaps in current ontology development methods regarding collaboration and negotiation in early development phases.

2008

Goat milk free fatty acid characterization during conventional and ohmic heating pasteurization

Autores
Pereira, RN; Martins, RC; Vicente, AA;

Publicação
JOURNAL OF DAIRY SCIENCE

Abstract
The disruption of the milk fat globule membrane can lead to an excessive accumulation of free fatty acids in milk, which is frequently associated with the appearance of rancid flavors. Solid-phase microextraction and gas chromatography techniques have been shown to be useful tools in the quantification of individual free fatty acids in dairy products providing enough sensitivity to detect levels of rancidity in milk. Therefore, the aim of this study was to characterize the short-chain and medium-chain free fatty acid profile in i) raw untreated goat milk; ii) raw goat milk passing through pumps and heating units (plate-and-frame heat exchanger and ohmic heater); and iii) processed goat milk by conventional and ohmic pasteurization to determine the influence of each treatment in the final quality of the milk. Multivariate statistical analysis has shown that the treatments studied were not responsible for the variability found on free fatty acid contents. In particular, it was possible to conclude that ohmic pasteurization at 72 C for 15 s did not promote an extended modification of free fatty acid contents in goat milk when compared with that of conventional pasteurization. Furthermore, principal component analysis showed that the capric acid can be used to discriminate goat's milk with different free fatty acid concentrations. Hierarchical cluster analysis showed evidence of the existence of correlations between contents of short and medium chain free fatty acids in goat milk.

2008

Simulation-Based Optimization for Steel Stacking

Autores
Rei, RJ; Kubo, M; Pedroso, JP;

Publicação
MODELLING, COMPUTATION AND OPTIMIZATION IN INFORMATION SYSTEMS AND MANAGEMENT SCIENCES, PROCEEDINGS

Abstract
In many sectors of industry, manufacturers posses warehouses where finished goods are stored, awaiting to fulfill a client order. We present a situation where these items are characterized by release and due dates, i.e. warehouse arrival for storage and client delivery, respectively. The warehouse has a number of positions available, where item can be placed on top of each other, forming stacks, For item manipulation, there is a single a stacking crane, able to carry one item at time. When in a given stack an item at the top is due at a date later than some item below it, it must be relocated to another stack, so that the item below can be delivered. In this problem the objective is to minimize the number of movements made by the crane.

2008

Relevant principal component analysis applied to the characterisation of Portuguese heather honey

Autores
Martins, RC; Lopes, VV; Valentao, P; Carvalho, JCMF; Isabel, P; Amaral, MT; Batista, MT; Andrade, PB; Silva, BM;

Publicação
NATURAL PRODUCT RESEARCH

Abstract
The main purpose of this study was the characterisation of 'Serra da Lousa' heather honey by using novel statistical methodology, relevant principal component analysis, in order to assess the correlations between production year, locality and composition. Herein, we also report its chemical composition in terms of sugars, glycerol and ethanol, and physicochemical parameters. Sugars profiles from 'Serra da Lousa' heather and 'Terra Quente de Tras-os-Montes' lavender honeys were compared and allowed the discrimination: 'Serra da Lousa' honeys do not contain sucrose, generally exhibit lower contents of turanose, trehalose and maltose and higher contents of fructose and glucose. Different localities from 'Serra da Lousa' provided groups of samples with high and low glycerol contents. Glycerol and ethanol contents were revealed to be independent of the sugars profiles. These data and statistical models can be very useful in the comparison and detection of adulterations during the quality control analysis of 'Serra da Lousa' honey.

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