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Publicações

2015

Compressive Classification: Where Wireless Communications Meets Machine Learning

Autores
Rodrigues, M; Nokleby, M; Renna, F; Calderbank, R;

Publicação
Compressed Sensing and its Applications

Abstract
This chapter introduces Shannon-inspired performance limits associated with the classification of low-dimensional subspaces embedded in a high-dimensional ambient space from compressive and noisy measurements. In particular, it introduces the diversity-discrimination tradeoff that describes the interplay between the number of classes that can be separated by a compressive classifier-measured via the discrimination gain-and the performance of such a classifier-measured via the diversity gain-and the relation of such an interplay to the underlying problem geometry, including the ambient space dimension, the subspaces dimension, and the number of compressive measurements. Such a fundamental limit on performance is derived from a syntactic equivalence between the compressive classification problem and certain wireless communications problems. This equivalence provides an opportunity to cross-pollinate ideas between the wireless information theory domain and the compressive classification domain. This chapter also demonstrates how theory aligns with practice in a concrete application: face recognition from a set of noisy compressive measurements.

2015

GAME DESIGN AND THE GAMIFICATION OF CONTENT: ASSESSING A PROJECT FOR LEARNING SIGN LANGUAGE

Autores
Bidarra, J; Escudeiro, P; Escudeiro, N; Reis, R; Baltazar, AB; Rodrigues, P; Lopes, J; Norberto, M; Barbosa, M;

Publicação
EDULEARN15: 7TH INTERNATIONAL CONFERENCE ON EDUCATION AND NEW LEARNING TECHNOLOGIES

Abstract
This paper discusses the concepts of game design and gamification of content, based on the development of a serious game aimed at making the process of learning sign language enjoyable and interactive. In this game the player controls a character that interacts with various objects and non player characters, with the aim of collecting several gestures from the Portuguese Sign Language corpus. The learning model used pushes forward the concept of gamification as a learning process valued by students and teachers alike, and illustrates how it may be used as a personalized device for amplifying learning. Our goal is to provide a new methodology to involve students and general public in learning specific subjects using a ludic, participatory and interactive approach supported by ICT-based tools. Thus, in this paper we argue that perhaps some education processes could be improved by adding the gaming factor through technologies that are able to involve students in a way that is more physical (e.g. using Kinect and sensor gloves), so learning becomes more intense and memorable.

2015

Optimal Behavior of Demand Response Aggregators in Providing Balancing and Ancillary Services in Renewable-Based Power Systems

Autores
Heydarian Forushani, E; Golshan, MEH; Shafie Khah, M; Catalao, JPS;

Publicação
TECHNOLOGICAL INNOVATION FOR CLOUD-BASED ENGINEERING SYSTEMS

Abstract
Due to the limited predictability and associated uncertainty of renewable energy resources, renewable-based electricity systems are confronted with instability problems. In such power systems, implementation of Demand Response (DR) programs not only can improve the system stability but also enhances market efficiency and system reliability. By implementing cloud-based engineering systems the utilization of DR will be increased and consequently DR will play a more crucial role in the future. Therefore, DR aggregators can efficiently take part in energy, balancing and ancillary services markets. In this paper, a model has been developed to optimize the behavior of a DR aggregator to simultaneously participate in the mentioned markets. To this end, the DR aggregator optimizes its offering/bidding strategies based on the contracts with its customers. In the proposed model, uncertainties of renewable energy resources and the prices of electricity markets are considered. Numerical studies show the effectiveness of the proposed model.

2015

Multi-Target Regression from High-Speed Data Streams with Adaptive Model Rules

Autores
Duarte, J; Gama, J;

Publicação
PROCEEDINGS OF THE 2015 IEEE INTERNATIONAL CONFERENCE ON DATA SCIENCE AND ADVANCED ANALYTICS (IEEE DSAA 2015)

Abstract
Many real life prediction problems involve predicting a structured output. Multi-target regression is an instance of structured output prediction whose task is to predict for multiple target variables. Structured output algorithms are usually computationally and memory demanding, hence are not suited for dealing with massive amounts of data. Most of these algorithms can be categorized as local or global methods. Local methods produce individual models for each output component and combine them to produce the structured prediction. Global methods adapt traditional learning algorithms to predict the output structure as a whole. We propose the first rule-based algorithm for solving multi-target regression problems from data streams. The algorithm builds on the adaptive model rules framework. In contrast to the majority of the structured output predictors, this particular algorithm does not fall into the local and global categories. Instead, each rule specializes on related subsets of the output attributes. To evaluate the performance of the proposed algorithm, two other rule-based algorithms were developed, one using the local strategy and the other using the global strategy. These methods were compared considering their prediction error, memory usage, computational time, and model complexity. Experimental results on synthetic and real data show that the local-strategy algorithm usually obtains the lowest error. However, the proposed and the global-strategy algorithms use much less memory and run significantly much faster at the cost of a slightly increase in the error, which make them very attractive when computation resources are an important factor. Also, the models produced by the latter approaches are much easier to understand since considerably less rules are produced.

2015

Resampling strategies for regression

Autores
Torgo, L; Branco, P; Ribeiro, RP; Pfahringer, B;

Publicação
EXPERT SYSTEMS

Abstract
Several real world prediction problems involve forecasting rare values of a target variable. When this variable is nominal, we have a problem of class imbalance that was thoroughly studied within machine learning. For regression tasks, where the target variable is continuous, few works exist addressing this type of problem. Still, important applications involve forecasting rare extreme values of a continuous target variable. This paper describes a contribution to this type of tasks. Namely, we propose to address such tasks by resampling approaches that change the distribution of the given data set to decrease the problem of imbalance between the rare target cases and the most frequent ones. We present two modifications of well-known resampling strategies for classification tasks: the under-sampling and the synthetic minority over-sampling technique (SMOTE) methods. These modifications allow the use of these strategies on regression tasks where the goal is to forecast rare extreme values of the target variable. In an extensive set of experiments, we provide empirical evidence for the superiority of our proposals for these particular regression tasks. The proposed resampling methods can be used with any existing regression algorithm, which means that they are general tools for addressing problems of forecasting rare extreme values of a continuous target variable.

2015

A logic for n-dimensional hierarchical refinement

Autores
Madeira, A; Martins, MA; Barbosa, LS;

Publicação
ELECTRONIC PROCEEDINGS IN THEORETICAL COMPUTER SCIENCE

Abstract
Hierarchical transition systems provide a popular mathematical structure to represent state-based software applications in which different layers of abstraction are represented by inter-related state machines. The decomposition of high level states into inner sub-states, and of their transitions into inner sub-transitions is common refinement procedure adopted in a number of specification formalisms. This paper introduces a hybrid modal logic for k-layered transition systems, its first-order standard translation, a notion of bisimulation, and a modal invariance result. Layered and hierarchical notions of refinement are also discussed in this setting.

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