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Publicações

2007

Barriers (and solutions...) to very high wind penetration in power systems

Autores
Estanqueiro, AI; de Jesus, JMF; Ricardo, J; dos Santos, A; Lopes, JAP;

Publicação
2007 IEEE POWER ENGINEERING SOCIETY GENERAL MEETING, VOLS 1-10

Abstract
In this paper the existing technical barriers that prevent the accomplishment of a very high wind generation penetration in a power system are presented. Since several countries and regions in Europe are already experiencing such high wind penetration or, as a minimum, planning their grids and operation strategies to cope with wind penetration from a high to a very high level, the solutions already identified for the most common constraints are also identified.

2007

Using an OPF like approach to define the operational strategy of a wind park under a system operator control

Autores
Moyano, CF; Pecas Lopes, JAP;

Publicação
2007 IEEE LAUSANNE POWERTECH, VOLS 1-5

Abstract
This paper presents a formulation for an Optimal Power Flow problem that includes the DFIG wind generator reactive power characteristics in order to obtain set points that consider wind turbines loading capabilities. This approach can be adopted at the wind park control level to define the active and reactive set points following requests from the wind park dispatch centers.

2007

Evaluation of contrast enhancement filters for lung nodule detection

Autores
Pereira, CS; Mendonca, AM; Campilho, A;

Publicação
IMAGE ANALYSIS AND RECOGNITION, PROCEEDINGS

Abstract
The aim of this paper is to evaluate and compare the performance of three convergence index (CI) filters when applied to the enhancement of chest radiographs, aiming at the detection of lung nodules. One of these filters, the sliding band filter (SBF), is the proposal of an innovative operator, while the other two CI class members, the iris filter (IF) and the adaptive ring filter (ARF), are already known in this application. To demonstrate the adequacy of the new filter for the enhancement of chest x-ray images, we calculated several figures of merit with the goal of comparing (i) the contrast enhancement capability of the filters, and (ii) the behavior of the filters for the detection of lung nodules. The results obtained for 154 images with nodules of the JSRT database show that the SBF outperforms both the IF and ARF. The proposed filter demonstrated to be a promising enhancement method, thus justifying its use in the first stage of a computer-aided diagnosis system for the detection of lung nodules.

2007

Simultaneous tuning of power system stabilizers installed in DFIG-based wind generation

Autores
Mendonca, A; Lopes, JAP;

Publicação
2007 IEEE LAUSANNE POWERTECH, VOLS 1-5

Abstract
This paper addresses the problem of large wind power integration and its impact on damping of the electromechnnical modes of oscillation. The viability of the doubly fed induction generator (DFIG) supplying additional damping is discussed and power system stabilizers (PSS) installed in DFIG wind power generators are simultaneously tuned to increase damping levels of a multimachine system.

2007

Towards the Integration of Visual and Formal Models for GUI Testing

Autores
Paiva, ACR; Faria, JCP; Vidal, RFAM;

Publicação
Electronic Notes in Theoretical Computer Science

Abstract
This paper presents an approach to diminish the effort required in GUI modelling and test coverage analysis within a model-based GUI testing process. A familiar visual notation a subset of UML with minor extensions is used to model the structure, behaviour and usage of GUIs at a high level of abstraction and to describe test adequacy criteria. The GUI visual model is translated automatically to a model-based formal specification language (e.g., Spec{music sharp sign}), hiding formal details from the testers. Then, additional behaviour may be added to the formal model to be used as a test oracle. The adequacy of the test cases generated automatically from the formal model is accessed based on the structural coverage of the UML behavioural diagrams.

2007

Detection of lung nodule candidates in chest radiographs

Autores
Pereira, CS; Fernandes, H; Mendonca, AM; Campilho, A;

Publicação
Pattern Recognition and Image Analysis, Pt 2, Proceedings

Abstract
This paper presents an automated method for the selection of a set of lung nodule candidates, which is the first stage of a computer-aided diagnosis system for the detection of pulmonary nodules. An innovative operator, called sliding band filter (SBF), is used for enhancing the lung field areas. In order to reduce the influence of the blood vessels near the mediastinum, this filtered image is multiplied by a mask that assigns to each lung field point an a priori probability of belonging to a nodule. The result is further processed with a watershed segmentation method that divides each lung field into a set of non-overlapping areas. Suspicious nodule locations are associated with the regions containing the highest regional maximum values. The proposed method, whose result is an ordered set of lung nodule candidate regions, was evaluated on the 247 images of the JSRT database with very promising results.

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