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Publicações

2005

Defining control strategies for analysing microgrids islanded operation

Autores
Lopes, JAP; Moreira, CL; Madureira, AG;

Publicação
2005 IEEE Russia Power Tech, PowerTech

Abstract
The main objective of this paper is to present the development of microsource modelling and the definition of control strategies to be adopted to evaluate the feasibility of operation of a microgrid when it becomes isolated. Normally, the microgrid operates in interconnected mode with the MV network, however scheduled or forced isolation can take place. In such conditions, the microgrid must have the ability to operate stably and autonomously. An evaluation of the need of storage devices and load-shedding strategies is included in the paper.

2005

View learning for statistical relational learning: With an application to mammography

Autores
Davis, J; Burnside, E; Dutra, I; Page, D; Ramakrishnan, R; Costa, VS; Shavlik, J;

Publicação
IJCAI International Joint Conference on Artificial Intelligence

Abstract
Statistical relational learning (SRL) constructs probabilistic models from relational databases. A key capability of SRL is the learning of arcs (in the Bayes net sense) connecting entries in different rows of a relational table, or in different tables. Nevertheless, SRL approaches currently are constrained to use the existing database schema. For many database applications, users find it profitable to define alternative "views" of the database, in effect defining new fields or tables. Such new fields or tables can also be highly useful in learning. We provide SRL with the capability of learning new views.

2005

New mechanism of vacuum radiation from non-accelerated moving boundaries

Autores
Guerreiro, A; Mendonca, JT; Martins, AM;

Publicação
JOURNAL OF OPTICS B-QUANTUM AND SEMICLASSICAL OPTICS

Abstract
We derive the effects of time refraction in a dispersive medium. A new type of radiation process is described that extends the concept of Unruh radiation to a non-accelerated but superluminal perturbation of the optical properties of a medium. The case of a plasma is considered as an example.

2005

Discordancy test for the bipolar Watson distribution defined on the hypersphere

Autores
Figueiredo, A; Gomes, P;

Publicação
COMMUNICATIONS IN STATISTICS-SIMULATION AND COMPUTATION

Abstract
As the Watson distribution is much used for modeling axial data, it is important to investigate the existence of a possible outlier in samples from this distribution. So, we generalize to the hypersphere a test of discordancy of an outlier or several outliers en bloc available for the Watson distribution defined on the sphere. We also evaluate the performance of the test for some cases with the usual types of alternatives.

2005

Stress profiling of arc-induced long-period gratings written in pure-silica-core fibers

Autores
Rego, G; Carvalho, JCC; Marques, PVS;

Publicação
17th International Conference on Optical Fibre Sensors, Pts 1 and 2

Abstract
Long-period gratings were written in a pure-silica-core fiber using the electric arc technique. To assess the influence of stress relaxation on grating formation, tomographic stress measurements were performed inside the grating. No stress annealing could be observed within the accuracy of the stress measurement, suggesting a negligible photo-elastic contribution to the arc-induced perturbation of the index profile. In contrast, stress relaxation was found inside a splice of pure-silica-core fiber where discharge conditions are different, indicating the general potential to alter the fibers stress and thus the index profile using an electric arc.

2005

Interference caused by the insertion of an h-BEB station in standard shared-Ethernet networks: Simulation analysis

Autores
Moraes, R; Vasques, F;

Publicação
MODELLING AND SIMULATION 2005

Abstract
In this paper, it is presented the simulation analysis of an enhanced algorithm for the collision resolution in shared Ethernet networks. Such algorithm, referred as high priority Binary Exponential Backoff (h-BEB), provides high priority traffic separation, enabling the Support of real-time communications. One of the main features of the h-BEB algorithm is to enable the coexistence in the same network segment of Ethernet standard stations with h-BEB modified stations, by imposing higher priority for the transfer of h-BEB messages (privileged traffic). The simulation analysis shows that the proposed traffic separation guarantees a predictable and significantly smaller access delay for the h-BEB station, when compared with the access delay for standard Ethernet stations. The simulation analysis also shows that the h-BEB traffic must be tightly controlled, as it has a high interference level over the non-real-time traffic. Otherwise, if the load generated by the h-BEB station is not closely controlled, the standard Ethernet stations may experience extended access delays.

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