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Publicações

2006

A pipelined data-parallel algorithm for ILP

Autores
Fonseca, NA; Silva, F; Costa, VS; Camacho, R;

Publicação
2005 IEEE INTERNATIONAL CONFERENCE ON CLUSTER COMPUTING (CLUSTER)

Abstract
The amount of data collected and stored in databases is growing considerably for almost all areas of human activity. Processing this amount of data is very expensive, both humanly and computationally. This justifies the increased interest both on the automatic discovery of useful knowledge from databases, and on using parallel processing for this task. Multi Relational Data Mining (MRDM) techniques, such as Inductive Logic Programming (ILP), can learn rules from relational databases consisting of multiple tables. However current ILP systems are designed to run in main memory and can have long running times. We propose a pipelined data-parallel algorithm for ILP. The algorithm was implemented and evaluated on a commodity PC cluster with 8 processors. The results show that our algorithm yields excellent speedups, while preserving the quality of learning.

2006

GANS: A Signalling Framework for Dynamic Interworking between Heterogeneous Networks

Autores
Akhtar, N; Campos, R; Kappler, C; Paakkonen, P; Poyhonen, P; Zhou, D;

Publicação
2006 IEEE 64TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6

Abstract
There is a growing trend towards convergence of telecommunication and data networks in order to support a richer set of services and applications. At the same time, increasing diversity and density of network access technologies has made the goal of providing connectivity anytime and anywhere a real possibility. Another important development is the emergence of small, low-complexity user owned networks, such as Personal Area Networks and Body Area Networks. Dynamic interworking, also known as network composition, between networks of different types and sizes is essential in the push towards convergence, as well as to realize truly seamless connectivity between heterogeneous access networks. Dynamic interworking requires signalling between different elements of the control planes of the different networks in order to coordinate the control functions and resources of the networks concerned. In this paper, we present the Generic Ambient Network Signalling protocol suite to address the diverse signalling requirements for dynamic interworking of networks.

2006

Wavelet analysis of the Lisbon and Gibraltar North Atlantic Oscillation winter indices

Autores
Barbosa, S; Silva, ME; Fernandes, MJ;

Publicação
INTERNATIONAL JOURNAL OF CLIMATOLOGY

Abstract
The North Atlantic Oscillation (NAO) is one of the most important climatic patterns in the Northern Hemisphere. Indices based on the normalised pressure difference between Iceland and a Southern station, such as Lisbon or Gibraltar, have been defined in order to describe NAO temporal evolution. Although exhibiting interannual and decadal variability, the signals are statistically rather featureless and therefore it is difficult to discriminate between different types of stochastic models. In this study, Lisbon and Gibraltar NAO winter indices are analysed using the discrete wavelet transform discrete wavelet transform(DWT). A multi-resolution analysis (MRA) is carried out for a scale-based description of the indices and the wavelet spectrum is used to identify and estimate long-range dependence. The degree of association of the two NAO indices is assessed by estimating the wavelet covariance for the two signals. The scale-based approach inherent to the discrete wavelet methodology allows a scale-by-scale comparison of the signals and shows that although the short-term temporal pattern is very similar for both indices, the long-term temporal structure is distinct. Furthermore, the degree of persistence or 'memory' is also distinct: the Lisbon index is best described by a long-range dependent (LRD) process, while the Gibraltar index is adequately described by a short-range process. Therefore, while trend features in the Lisbon NAO index may be explainable by long-range dependence alone, with no need to invoke external factors, for the Gibraltar index such features cannot be interpreted as resulting only from internal variability through long-range dependence. Copyright (C) 2006 Royal Meteorological Society.

2006

Long-range dependence in North Atlantic sea level

Autores
Barbosa, SM; Fernandes, MJ; Silva, ME;

Publicação
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS

Abstract
Sea level is an important parameter in climate and oceanographic applications. In this work the scaling behavior of sea level is analyzed from time series of sea level observations. The wavelet domain is particularly attractive for the identification of scaling behavior in an observed time series. The wavelet spectrum from a scale-by-scale wavelet analysis of variance reproduces in the wavelet domain the power laws underlying a scaling process, allowing the estimation of the scaling exponent from the slope of the wavelet spectrum. Here the scaling exponent is estimated in the wavelet domain for time series of sea level observations in the North Atlantic: at coastal sites from tide gauges, covering 50 years of monthly measurements, and in the open ocean from satellite altimetry, covering 12 years of satellite measurements at 10 days intervals. Both tide gauge and altimetry time series exhibit scaling behavior. Furthermore, the degree of stochastic persistence is spatially coherent and distinct at the coast and in the open ocean. Near the coast, the stochastic structure of the sea level observations is characterized by long-range dependence with a moderate degree of persistence. Larger values of the scaling exponent, consistent with weaker persistence, are concentrated in the northern Atlantic. At mid-latitudes the stochastic dependence of sea level observations is characterized by strong persistence in the form of strong long-range and 1/f dependence.

2006

Scalability of name resolution for ambient networks

Autores
Paakkonen, P; Akhtar, N; Campos, R; Kappler, C; Poyhonen, P; Zhou, D;

Publicação
WIRED/WIRELESS INTERNET COMMUNICATIONS, PROCEEDINGS

Abstract
The convergence of mobile domain and data networks has been under focus in the standardization forums. However, dynamic interworking of wired infrastructure, wireless access systems and small scale Personal Area Networks has been challenging due to their heterogeneous nature. One of the most important problems to be solved is name resolution between different terminals and networks. This paper presents a new mechanism for name resolution, which relies on existing naming mechanisms. In particular the focus is on the scalability of the solution from signaling load and latency point of view.

2006

Data mining and visualization of the Spanish electricity market [Minería y visualización de datos del mercado eléctrico español]

Autores
Sánchez Úbeda, EF; Muñoz, A; Villar, J;

Publicação
Inteligencia Artificial

Abstract

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