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Publications

2013

On evaluating stream learning algorithms

Authors
Gama, J; Sebastiao, R; Rodrigues, PP;

Publication
MACHINE LEARNING

Abstract
Most streaming decision models evolve continuously over time, run in resource-aware environments, and detect and react to changes in the environment generating data. One important issue, not yet convincingly addressed, is the design of experimental work to evaluate and compare decision models that evolve over time. This paper proposes a general framework for assessing predictive stream learning algorithms. We defend the use of prequential error with forgetting mechanisms to provide reliable error estimators. We prove that, in stationary data and for consistent learning algorithms, the holdout estimator, the prequential error and the prequential error estimated over a sliding window or using fading factors, all converge to the Bayes error. The use of prequential error with forgetting mechanisms reveals to be advantageous in assessing performance and in comparing stream learning algorithms. It is also worthwhile to use the proposed methods for hypothesis testing and for change detection. In a set of experiments in drift scenarios, we evaluate the ability of a standard change detection algorithm to detect change using three prequential error estimators. These experiments point out that the use of forgetting mechanisms (sliding windows or fading factors) are required for fast and efficient change detection. In comparison to sliding windows, fading factors are faster and memoryless, both important requirements for streaming applications. Overall, this paper is a contribution to a discussion on best practice for performance assessment when learning is a continuous process, and the decision models are dynamic and evolve over time.

2013

On the Development and Usability of a Diagram-based Collaborative Brainstorming Component

Authors
Azevedo, D; Fonseca, B; Paredes, H; Lukosch, S; Janeiro, J; Briggs, RO;

Publication
JOURNAL OF UNIVERSAL COMPUTER SCIENCE

Abstract
The need for computer-supported collaboration has grown over the last years and made collaboration an important factor within organizations. This trend has resulted in the development of a variety of tools and technologies to support the various forms of collaboration. Many collaborative processes, e. g. strategy building, scenario analysis, root cause analysis and requirements engineering, require various collaboration support tools. Data flow, fishbone and brainstorming diagrams, play an important role within these synchronous collaborative applications to create, evaluate, elaborate, discuss, and revise graphical models. Currently, the necessary tools are not integrated and flexible enough to support such processes. In this paper, a synchronous collaborative brainstorming diagram editor integrated in a flexible group support system is described. This approach goes beyond the current state of the art as it can be seamlessly integrated with other collaboration support tools such as text-based brainstorming or voting. The usability of the taken approach is evaluated within a case study on collaborative learning.

2013

Práticas pedagógicas na perspectiva do hibridismo tecnológico digital

Authors
Backes, L; Schlemmer, E;

Publication
Revista Diálogo Educacional

Abstract
Atualmente, as Tecnologias Digitais (TD) apresentam inúmeras possibilidades para a interação, a comunicação e a representação do conhecimento, favorecendo a configuração de espaços digitais virtuais de convivência, que potencializam os processos de ensinar e de aprender, numa perspectiva de hibridismo tecnológico digital. Nesse contexto, emergem questões como: quais são os aspectos no processo de ensinar e de aprender que contribuem para a configuração dos espaços de convivência no contexto do hibridismo tecnológico digital? Quais as características da prática pedagógica que podem favorecer uma formação para este tempo e este espaço? Para tanto, foram desenvolvidos processos de formação no Ensino Superior, contextos Brasil e França, na perspectiva do hibridismo tecnológico digital, o qual comportou as seguintes TD: ambiente virtual de aprendizagem; comunicador instantâneo; blog e metaverso. Os processos formativos se desenvolveram por meio da Metodologia de Projetos de Aprendizagem baseado em Problema (Brasil) e da Metodologia Pedagógica de Estudo de Caso (França). Os dados empíricos são as representações expressas nas TD, no processo de interação dos estudantes, submetidas à metodologia de análise de conteúdo. A análise de conteúdo, realizada no contexto das unidades de análise, passou por tratamentos de natureza qualitativa, quantitativa e, novamente, qualitativa. Esta análise complexa nos instigou à reflexão sobre as práticas pedagógicas como possibilidade de problematizar a realidade atual, utilizando as TD de maneira congruente. Assim, os estudantes são instigados a (re)significar a realidade atual, numa condição de responsabilidade em relação às TD, a fim de encontrar alternativas para a emancipação na construção de novos conhecimentos. 

2013

Energy-Efficient Packet Relaying in Wireless Image Sensor Networks Exploiting the Sensing Relevancies of Source Nodes and DWT Coding

Authors
Costa, DG; Guedes, LA; Vasques, F; Portugal, P;

Publication
J. Sensor and Actuator Networks

Abstract
When camera-enabled sensors are deployed for visual monitoring, a new set of innovative applications is allowed, enriching the use of wireless sensor network technologies. In these networks, energy-efficiency is a highly desired optimization issue, mainly because transmission of images and video streams over resource-constrained sensor networks is more stringent than transmission of conventional scalar data. Due to the nature of visual monitoring, that follows a directional sensing model, camera-enabled sensors may have different relevancies for the application, according to the desired monitoring tasks and the current sensors' poses and fields of view. Exploiting this concept, each data packet may be associated with a priority level related to the packet's origins, which may be in turn mapped to an energy threshold level. In such way, we propose an energy-efficient relaying mechanism where data packets are only forwarded to the next hop if the associated energy threshold level is below the current energy level of the relaying node. Thus, packets from low-relevant source nodes will be silently dropped when the current energy level of intermediate nodes run below the pre-defined thresholds. Doing so, energy is saved potentially prolonging the network lifetime. Besides the sensing relevancies of source nodes, the relevance of DWT subbands for reconstruction of original images is also considered. This allows the creation of a second level of packet prioritization, assuring a minimal level of image quality even for the least relevant source nodes. We performed simulations for the proposed relaying mechanism, assessing the expected performance over a traditional relaying paradigm.

2013

Lean management methods in product development: A case study

Authors
Soares, D; Bastos, J; Gavazzo, D; Pereira, JP; Baptista, AJ;

Publication
Lecture Notes in Mechanical Engineering

Abstract
The current reality of intense competition has forced many companies to increase their performance and competitive advantages by pursuing innovation and improving and streamlining internal methods of designing products and processes. With shortening of product life cycle, in order for companies to survive, the need for a continuous stream of multiple innovations over time has arisen. However, the resources consumed by companies, whilst developing a product or process, are increasingly high, even in integrated approaches, and often the finished product or process arrives too late to provide the company with an edge over its competitors. Due to the large impact Lean philosophy has had in recent decades, within the manufacturing area, through the increase of efficiency and generation of continuous improvement, more companies have progressively applied Lean methods in their units of product and process development. This paper seeks to present a reference model for Lean implementation in the areas of product and process development in order to support companies in their path to streamline and make their innovative processes more efficient. The proposed reference model includes a concrete case study example that helps to explain the main concepts behind the proposed approach. © Springer International Publishing Switzerland 2013.

2013

Review of fiber-optic pressure sensors for biomedical and biomechanical applications

Authors
Roriz, P; Frazao, O; Lobo Ribeiro, AB; Santos, JL; Simoes, JA;

Publication
JOURNAL OF BIOMEDICAL OPTICS

Abstract
As optical fibers revolutionize the way data is carried in telecommunications, the same is happening in the world of sensing. Fiber-optic sensors (FOS) rely on the principle of changing the properties of light that propagate in the fiber due to the effect of a specific physical or chemical parameter. We demonstrate the potentialities of this sensing concept to assess pressure in biomedical and biomechanical applications. FOSs are introduced after an overview of conventional sensors that are being used in the field. Pointing out their limitations, particularly as minimally invasive sensors, is also the starting point to argue FOSs are an alternative or a substitution technology. Even so, this technology will be more or less effective depending on the efforts to present more affordable turnkey solutions and peer-reviewed papers reporting in vivo experiments and clinical trials. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.JBO.18.5.050903]

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