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Publications

2013

Entropy and compression: two measures of complexity

Authors
Henriques, T; Goncalves, H; Antunes, L; Matias, M; Bernardes, J; Costa Santos, C;

Publication
JOURNAL OF EVALUATION IN CLINICAL PRACTICE

Abstract
Rationale, aims and objectivesTraditional complexity measures are used to capture the amount of structured information present in a certain phenomenon. Several approaches developed to facilitate the characterization of complexity have been described in the related literature. Fetal heart rate (FHR) monitoring has been used and improved during the last decades. The importance of these studies lies on an attempt to predict the fetus outcome, but complexity measures are not yet established in clinical practice. In this study, we have focused on two conceptually different measures: Shannon entropy, a probabilistic approach, and Kolmogorov complexity, an algorithmic approach. The main aim of the current investigation was to show that approximation to Kolmogorov complexity through different compressors, although applied to a lesser extent, may be as useful as Shannon entropy calculated by approximation through different entropies, which has been successfully applied to different scientific areas. MethodsTo illustrate the applicability of both approaches, two entropy measures, approximate and sample entropy, and two compressors, paq8l and bzip2, were considered. These indices were applied to FHR tracings pertaining to a dataset composed of 48 delivered fetuses with umbilical artery blood (UAB) pH in the normal range (pH7.20), 10 delivered mildly acidemic fetuses and 10 moderate-to-severe acidemic fetuses. The complexity indices were computed on the initial and final segments of the last hour of labour, considering 5- and 10-minute segments. ResultsIn our sample set, both entropies and compressors were successfully utilized to distinguish fetuses at risk of hypoxia from healthy ones. Fetuses with lower UAB pH presented significantly lower entropy and compression indices, more markedly in the final segments. ConclusionsThe combination of these conceptually different measures appeared to present an improved approach in the characterization of different pathophysiological states, reinforcing the theory that entropies and compressors measure different complexity features. In view of these findings, we recommend a combination of the two approaches.

2013

A Pattern-Based Approach for GUI Modeling and Testing

Authors
Moreira, RMLM; Paiva, ACR; Memon, A;

Publication
2013 IEEE 24TH INTERNATIONAL SYMPOSIUM ON SOFTWARE RELIABILITY ENGINEERING (ISSRE)

Abstract
User Interface (UI) patterns are used extensively in the design of today's software. UI patterns embody commonly recurring solutions that solve common GUI design problems, such as "login," "file-open," and "search." Yet, testing of GUIs for functional correctness has largely ignored UI patterns. This paper formalizes the notion of a Pattern-Based Graphical User Interface (GUI) Testing method (PBGT) for systematizing and automating the GUI testing process. The space of all possible interactions with a GUI is typically very large. PBGT presents a new methodology to sample the input space using " UI Test Patterns," that embody commonly recurring solutions to test GUIs. Our empirical studies show that the PBGT methodology is effective in revealing faults in fielded GUIs.

2013

Comparing Two Class Composition Approaches

Authors
Barbosa, F; Aguiar, A;

Publication
EVALUATION OF NOVEL APPROACHES TO SOFTWARE ENGINEERING, ENASE 2013

Abstract
The presence of code replication can be a consequence of a lack in the composition mechanisms where classes are insufficient to reuse the code that is replicated. To extend the reuse of pieces of code some proposals have been made that try to compose classes using those pieces of code. In this paper we compare two of those approaches: Traits and Roles. We compare their compositions mechanisms and how we can use them to reduce code replication. To study the extent to which they reduce code replication we conducted a case study using the JHotDraw framework where we detect and remove code replication using each technique. Results from the case study show that roles have an advantage over traits, as they are capable of removing more code replication.

2013

ACM SIGCHI Symposium on Engineering Interactive Computing Systems, EICS'13, London, United Kingdom - June 24 - 27, 2013

Authors
Forbrig, P; Dewan, P; Harrison, M; Luyten, K;

Publication
EICS

Abstract

2013

RAC: A Freerider-Resilient, Scalable, Anonymous Communication Protocol

Authors
Mokhtar, SB; Berthou, G; Diarra, A; Quéma, V; Shoker, A;

Publication
IEEE 33rd International Conference on Distributed Computing Systems, ICDCS 2013, 8-11 July, 2013, Philadelphia, Pennsylvania, USA

Abstract
Enabling anonymous communication over the Internet is crucial. The first protocols that have been devised for anonymous communication are subject to freeriding. Recent protocols have thus been proposed to deal with this issue. However, these protocols do not scale to large systems, and some of them further assume the existence of trusted servers. In this paper, we present RAC, the first anonymous communication protocol that tolerates freeriders and that scales to large systems. Scalability comes from the fact that the complexity of RAC in terms of the number of message exchanges is independent from the number of nodes in the system. Another important aspect of RAC is that it does not rely on any trusted third party. We theoretically prove, using game theory, that our protocol is a Nash equilibrium, i.e, that freeriders have no interest in deviating from the protocol. Further, we experimentally evaluate RAC using simulations. Our evaluation shows that, whatever the size of the system (up to 100.000 nodes), the nodes participating in the system observe the same throughput. © 2013 IEEE.

2013

New methodology for the optimization of the management of wind farms, including energy storage

Authors
Dufo Lopez, R; Bernal Agustin, JL; Monteiro, C;

Publication
Applied Mechanics and Materials

Abstract
Storing energy on wind farms could improve the power generation curve, avoiding the problems associated with abrupt variations and the random nature of wind power. New batteries such as flow batteries or NaS batteries are suitable to be used in storing energy on wind farms in intervals of some hours. A new methodology for the optimization of the management of wind farms, including energy storage, is shown. The objective is to maximize the benefits of selling electricity to the grid within 24 hours. The genetic algorithm technique was used for the optimization. © (2013) Trans Tech Publications, Switzerland.

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