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Publications

Publications by CTM

2011

Stability of traveling pulses of cubic-quintic complex Ginzburg-Landau equation including intrapulse Raman scattering

Authors
Facao, M; Carvalho, MI;

Publication
PHYSICS LETTERS A

Abstract
The complex cubic-quintic Ginzburg-Landau equation (CGLE) admits a special type of solutions called eruption solitons. Recently, the eruptions were shown to diminish or even disappear if a term of intrapulse Raman scattering (IRS) is added, in which case, self-similar traveling pulses exist. We perform a linear stability analysis of these pulses that shows that the unstable double eigenvalues of the erupting solutions split up under the effect of IRS and, following a different trajectory, they move on to the stable half-plane. The eigenfunctions characteristics explain some eruptions features. Nevertheless, for some CGLE parameters, the IRS cannot cancel the eruptions, since pulses do not propagate for the required IRS strength.

2011

Measuring the Performance of Beat Tracking Algorithms Using a Beat Error Histogram

Authors
Davies, MEP; Degara, N; Plumbley, MD;

Publication
IEEE SIGNAL PROCESSING LETTERS

Abstract
We present a new evaluation method for measuring the performance of musical audio beat tracking systems. Central to our method is a novel visualization, the beat error histogram, which illustrates the metrical relationship between two qausi-periodic sequences of time instants: the output of beat tracking system and a set of ground truth annotations. To quantify beat tracking performance we derive an information theoretic statistic from the histogram. Results indicate that our method is able to measure performance with greater precision than existing evaluation methods and implicitly cater for metrical ambiguity in tapping sequences.

2011

Onset Event Decoding Exploiting the Rhythmic Structure of Polyphonic Music

Authors
Degara, N; Davies, MEP; Pena, A; Plumbley, MD;

Publication
IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING

Abstract
In this paper, we propose a rhythmically informed method for onset detection in polyphonic music. Music is highly structured in terms of the temporal regularity underlying onset occurrences and this rhythmic structure can be used to locate sound events. Using a probabilistic formulation, the method integrates information extracted from the audio signal and rhythmic knowledge derived from tempo estimates in order to exploit the temporal expectations associated with rhythm and make musically meaningful event detections. To do so, the system explicitly models note events in terms of the elapsed time between consecutive events and decodes the most likely sequence of onsets that led to the observed audio signal. In this way, the proposed method is able to identify likely time instants for onsets and to successfully exploit the temporal regularity of music. The goal of this work is to define a general framework to be used in combination with any onset detection function and tempo estimator. The method is evaluated using a dataset of music that contains multiple instruments playing at the same time, including singing and different music genres. Results show that the use of rhythmic information improves the commonly used adaptive thresholding onset detection method which only considers local information. It is also shown that the proposed probabilistic framework successfully exploits rhythmic information using different detection functions and tempo estimation algorithms.

2011

WiFIX

Authors
Campos, R; Oliveira, C; Ruela, J;

Publication
2011 Eighth International Conference on Wireless On-Demand Network Systems and Services

Abstract

2011

WiFIX+: A multicast solution for 802.11-based Wireless Mesh Networks

Authors
Campos, R; Oliveira, C; Ruela, J;

Publication
2011 8th International Conference on Wireless On-Demand Network Systems and Services, WONS 2011

Abstract
IEEE 802.11 is currently one of the main wireless technologies enabling ubiquitous Internet access. With the growing demand for wireless Internet access and the limited 802.11 radio range, 802.11-based Wireless Mesh Networks have been proposed as a flexible and cost-effective solution to extend the radio coverage of existing network infrastructures. Many solutions have been proposed to create Wireless Mesh Networks automatically. However, they are either too complex or deal with multicast traffic inefficiently using pure flooding. We propose a simple and efficient solution, called WiFIX+, to forward multicast traffic over 802.11-based Wireless Mesh Networks. It is based on WiFIX, an existing solution targeted at unicast traffic and extends it with new mechanisms. WiFIX+ was implemented and evaluated in a laboratorial test-bed. The experimental results obtained show that it outperforms IEEE 802.11s, the reference solution for 802.11-based Wireless Mesh Networks, as far as data throughput, delay, and packet loss are concerned. © 2010 IEEE.

2011

Non-contact Pulse Wave Velocity Assessment Using Optical Methods

Authors
Pereira, T; Cabeleira, M; Matos, P; Borges, E; Almeida, V; Pereira, HC; Cardoso, J; Correia, CMBA;

Publication
Biomedical Engineering Systems and Technologies - 4th International Joint Conference, BIOSTEC 2011, Rome, Italy, January 26-29, 2011, Revised Selected Papers

Abstract
The clinical relevance of pulse wave velocity (PWV), as an indicator of cardiac risk associated to arterial stiffness, has gained clinical relevance over the last years. Optic sensors are an attractive instrumental solution for this type of measurement due to their truly non-contact operation capability, which has the potential of an interference free measurement. The nature of the optically originated signals, however, poses new challenges to the designer, either at the probe design level as at the signal processing required to extract the timing information that yields PWV. In this work we describe the construction of two prototype optical probes and discuss their evaluation using three algorithms for pulse transit time (PTT) evaluation. Results, obtained in a dedicated test bench, that is also described, demonstrate the possibility of measuring pulse transit times as short as 1ms with less than 1% error. © Springer-Verlag Berlin Heidelberg 2013.

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