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Publications

2015

New Multi-Objective Decision Support Methodology to Solve Problems of Reconfiguration in the Electric Distribution Systems

Authors
Santos, SF; Paterakis, NG; Catalao, JPS;

Publication
TECHNOLOGICAL INNOVATION FOR CLOUD-BASED ENGINEERING SYSTEMS

Abstract
The distribution systems (DS) reconfiguration problem is formulated in this paper as a multi-objective mixed-integer linear programming (MILP) multi-period problem, enforcing that the obtained topology is radial in order to exploit several advantages those configurations offer. The effects of distributed generation (DG) and energy storage systems (ESS) are also investigated. To address the multi-objective problem, an improved implementation of the e-constraint method (AUGMECON-2) is used, providing an adequate representation of the Pareto set. The objective functions considered stand for the minimization of active power losses and the minimization of switching operations. The proposed methodology is tested using a real system based on the S. Miguel Island, Azores, Portugal. The potential uses of cloud-based engineering systems, both in terms of exploiting the enhanced decentralized computational opportunities they offer and of utilizing them in order to achieve communication and coordination between several entities that are engaged in DS, are thoroughly discussed.

2015

a-GIZO TFT neural modeling, circuit simulation and validation

Authors
Bahubalindruni, PG; Tavares, VG; Barquinha, P; Duarte, C; Cardoso, N; de Oliveira, PG; Martins, R; Fortunato, E;

Publication
SOLID-STATE ELECTRONICS

Abstract
Development time and accuracy are measures that need to be taken into account when devising device models for a new technology. If complex circuits need to be designed immediately, then it is very important to reduce the time taken to realize the model. Solely based on data measurements, artificial neural networks (ANNs) modeling methodologies are capable of capturing small and large signal behavior of the transistor, with good accuracy, thus becoming excellent alternatives to more strenuous modeling approaches, such as physical and semi-empirical. This paper then addresses a static modeling methodology for amorphous Gallium-Indium-Zinc-Oxide - Thin Film Transistor (a-GIZO TFT), with different ANNs, namely: multilayer perceptron (MLP), radial basis functions (RBF) and least squares-support vector machine (LS-SVM). The modeling performance is validated by comparing the model outcome with measured data extracted from a real device. In case of a single transistor modeling and under the same training conditions, all the ANN approaches revealed a very good level of accuracy for large- and small-signal parameters (g(m) and g(d)), both in linear and saturation regions. However, in comparison to RBF and LS-SVM, the MLP achieves a very acceptable degree of accuracy with lesser complexity. The impact on simulation time is strongly related with model complexity, revealing that MLP is the most suitable approach for circuit simulations among the three ANNs. Accordingly, MLP is then extended for multiple TFTs with different aspect ratios and the network implemented in Verilog-A to be used with electric simulators. Further, a simple circuit (inverter) is simulated from the developed model and then the simulation outcome is validated with the fabricated circuit response.

2015

Uncertainty Based Multi-Robot Cooperative Triangulation

Authors
Dias, A; Almeida, J; Lima, P; Silva, E;

Publication
ROBOCUP 2014: ROBOT WORLD CUP XVIII

Abstract
The paper presents a multi-robot cooperative framework to estimate the 3D position of dynamic targets, based on bearing-only vision measurements. The uncertainty of the observation provided by each robot equipped with a bearing-only vision system is effectively addressed for cooperative triangulation purposes by weighing the contribution of each monocular bearing ray in a probabilistic manner. The envisioned framework is evaluated in an outdoor scenario with a team of heterogeneous robots composed of an Unmanned Ground and Aerial Vehicle.

2015

BALANCE SHEET ANALYSIS OF CREDIT AND DEBT NETWORKS

Authors
Garrido, P; Campos, P; Dias, A;

Publication
ADVANCES IN COMPLEX SYSTEMS

Abstract
In this paper, we present a computing procedure to analyze a network of credit and debt among agents (nodes) from a standpoint of balance sheet dependencies. The aim is to develop a method to assess thoroughly the sensitivity of the network to potential individual insolvencies. For this purpose, given a state of the network, the insolvency of an agent is assumed and the cascade of provoked insolvencies is simulated. Exploring the matrix definition of the network, this is made systematically for all agents. Therefore, in only one run of the procedure, all the possible trajectories of insolvencies, each beginning in a different agent, are calculated. This allows spotting at a glance which agents are "systemically riskier". Determination of adequate capital levels can be made on a case basis by running the procedure repeatedly. This work contributes with two new aspects to the existing literature. First, given a known situation of a credit and debt network, a computing procedure is presented that allows to assess the network sensitivity to the exogenous insolvency of any of its nodes. Second, continued monitoring of a credit and debt network is computationally feasible. This "proof of concept" software can be extended into a tool useful for research and regulation, if the relevant information is made available.

2015

Temporal Segmentation of Digital Colposcopies

Authors
Fernandes, K; Cardoso, JS; Fernandes, J;

Publication
PATTERN RECOGNITION AND IMAGE ANALYSIS (IBPRIA 2015)

Abstract
Cervical cancer remains a significant cause of mortality in low-income countries. Digital colposcopy is a promising and inexpensive technology for the detection of cervical intraepithelial neoplasia. However, diagnostic sensitivity varies widely depending on the doctor expertise. Therefore, automation of this process is needed in both, detection and visualization. Colposcopies cover four steps: macroscopic view with magnifier white light, observation under green light, Hinselmann and Schiller. Also, there are transition intervals where the specialist manipulates the observed area. In this paper, we focus on the temporal segmentation of the video in these steps. Using our solution, physicians may focus on the step of interest and lesion detection tools can determine the interval to diagnose. We solved the temporal segmentation problem using Weighted Automata. Images were described by their chromacity histograms and labeled using a KNN classifier with a precision of 97%. Transition frames were recognized with a precision of 91 %.

2015

X-Ray: Monitoring and Analysis of Distributed Database Queries

Authors
Guimarães, P; Pereira, J;

Publication
DAIS

Abstract
The integration of multiple database technologies, including both SQL and NoSQL, allows using the best tool for each aspect of a complex problem and is increasingly sought in practice. Unfortunately, this makes it difficult for database developers and administrators to obtain a clear view of the resulting composite data processing paths, as they combine operations chosen by different query optimisers, implemented by different software packages, and partitioned across distributed systems. This work addresses this challenge with the X-Ray framework, that allows monitoring code to be added to a Java-based distributed system by manipulating its bytecode at runtime. The resulting information is collected in a NoSQL database and then processed to visualise data processing paths as required for optimising integrated database systems. This proposal is demonstrated with a distributed query over a federation of Apache Derby database servers and its performance evaluated with the standard TPC-C benchmark workload.

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