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Publicações

2016

Tapered optical fiber tip probes based on focused ion beam-milled Fabry-Perot microcavities

Autores
Andre, RM; Warren Smith, SC; Becker, M; Dellith, J; Rothhardt, M; Zibaii, MI; Latifi, H; Marques, MB; Bartelt, H; Frazao, O;

Publicação
NANOENGINEERING: FABRICATION, PROPERTIES, OPTICS, AND DEVICES XIII

Abstract
Focused ion beam technology is combined with dynamic chemical etching to create microcavities in tapered optical fiber tips, resulting in fiber probes for temperature and refractive index sensing. Dynamic chemical etching uses hydrofluoric acid and a syringe pump to etch standard optical fibers into cone structures called tapered fiber tips where the length, shape, and cone angle can be precisely controlled. On these tips, focused ion beam is used to mill several different types of Fabry-Perot microcavities. Two main cavity types are initially compared and then combined to form a third, complex cavity structure. In the first case, a gap is milled on the tapered fiber tip which allows the external medium to penetrate the light guiding region and thus presents sensitivity to external refractive index changes. In the second, two slots that function as mirrors are milled on the tip creating a silica cavity that is only sensitive to temperature changes. Finally, both cavities are combined on a single tapered fiber tip, resulting in a multi-cavity structure capable of discriminating between temperature and refractive index variations. This dual characterization is performed with the aid of a fast Fourier transform method to separate the contributions of each cavity and thus of temperature and refractive index. Ultimately, a tapered optical fiber tip probe with sub-standard dimensions containing a multi-cavity structure is projected, fabricated, characterized and applied as a sensing element for simultaneous temperature and refractive index discrimination.

2016

Multi-Objective Reconfiguration of Radial Distribution Systems Using Reliability Indices

Autores
Paterakis, NG; Mazza, A; Santos, SF; Erdinc, O; Chicco, G; Bakirtzis, AG; Catalao, JPS;

Publicação
IEEE TRANSACTIONS ON POWER SYSTEMS

Abstract
This paper deals with the distribution network reconfiguration problem in a multi-objective scope, aiming to determine the optimal radial configuration by means of minimizing the active power losses and a set of commonly used reliability indices formulated with reference to the number of customers. The indices are developed in a way consistent with a mixed-integer linear programming (MILP) approach. A key contribution of the paper is the efficient implementation of the epsilon-constraint method using lexicographic optimization in order to solve the multi-objective optimization problem. After the Pareto efficient solution set is generated, the resulting configurations are evaluated using a backward/forward sweep load-flow algorithm to verify that the solutions obtained are both non-dominated and feasible. Since the epsilon-constraint method generates the Pareto front but does not incorporate decision maker (DM) preferences, a multi-attribute decision making procedure, namely, the technique for order preference by similarity to ideal solution (TOPSIS) method, is used in order to rank the obtained solutions according to the DM preferences, facilitating the final selection. The applicability of the proposed method is assessed on a classical test system and on a practical distribution system.

2016

TweeProfiles3: visualization of spatio-temporal patterns on Twitter

Autores
Maia, A; Cunha, T; Soares, C; Abreu, PH;

Publicação
NEW ADVANCES IN INFORMATION SYSTEMS AND TECHNOLOGIES, VOL 1

Abstract
With the advent of social networking, a lot of user-specific, voluntarily provided data has been generated. Researchers and companies noticed the value that lied within those enormous amounts of data and developed algorithms and tools to extract patterns in order to act on them. TweeProfiles is an offline clustering tool that analyses tweets over multiple dimensions: spatial, temporal, content and social. This project was extended in TweeProfiles2 by enabling the processing of real-time data. In this work, we developed a visualization tool suitable for data streaming, using multiple widgets to better represent all the information. The usefulness of the developed tool for journalism was evaluated based on a usability test, which despite its reduced number of participants yielded good results.

2016

Self-regulated learning in higher education: Strategies adopted by computer programming students

Autores
Pedrosa D.; Cravino J.; Morgado L.; Barreira C.;

Publicação
International Symposium on Project Approaches in Engineering Education

Abstract
To help students overcome their learning difficulties in the transition from entry-level to advanced computer programming, developing an appropriate set of learning strategies, the SimProgramming teaching approach has been adopted at the University of Trás-os-Montes e Alto Douro (Portugal). This approach is based on four conceptual foundations: businesslike learning environment, self-regulated learning, co-regulated learning, and formative assessment. In this approach the students develop an activity based on problem-based learning, with a specific set of tasks based on those four conceptual foundations. The approach was implemented in two courses from the second and third curricular years of the bachelor programmes in Informatics Engineering and Information & Communication Technologies. We conducted semi-structured interviews with students (n=32) at the end of the courses, to try to identify the students’ strategies for self-regulation of learning in the activity developed within the SimProgramming approach. The main strategies identified were: organization, planning, time management, identification of difficulties, resolution of the difficulties encountered, work review, identification of the factors that influenced their motivation, and structure of the environment. The factors influencing the motivation most often identified by students were the impact of the assessment in the final course grade, the completion of the course, learning, skills development, and teamwork. Generally, students applied strategies to solve the difficulties, in particular by searching for social help and information search. Procrastination was also often identified by students. Strategies of time management, transformation of information, in-depth review, self-reflection, and self-evaluation were referenced scantily. We found that students changed some of their strategies from one course edition to the next. We conclude by recommending the development of educational practices to help students review their work, treat and process the information they find, conduct self-reflection and self-evaluation of their performance during tasks, adopt concentration strategies, and become aware of their specific difficulties.

2016

Empirical Evaluation of the ProcessPAIR Tool for Automated Performance Analysis

Autores
Raza, M; Faria, JP; Salazar, R;

Publicação
SEKE

Abstract
Software development processes can generate significant amounts of data that can be periodically analyzed to identify performance problems, determine their root causes and devise improvement actions. However, conducting that analysis manually is challenging because of the potentially large amount of data to analyze and the effort and expertise required. ProcessPAIR is a novel tool designed to help developers analyze their performance data with less effort, by automatically identifying and ranking performance problems and potential root causes. The analysis is based on performance models derived from the performance data of a large community of developers. In this paper, we present the results of an experiment conducted in the context of Personal Software Process (PSP) training, to show that ProcessPAIR is able to accurately identify and rank performance problems and potential root causes of individual developers so that subsequent manual analysis for the identification of deeper causes and improvement actions can be properly focused.

2016

Integration; of energy storage in LV grid normal and emergency operation

Autores
Marques, M; Bessa, R; Moreira, C; Mousinho, P; Gouveia, C; Gerlich, M; Leiria, A; Madureira, A; Rodriguez, S;

Publicação
IET Conference Publications

Abstract
This paper presents the approach followed under project SENSIBLE to prove, in field-test scenarios, the benefits of integrating and coordinating small-scale storage devices to: (i) reduce the impact of Distributed Renewable Energy Sources in the Low Voltage grid and (ii) support the transition and the operation in islanding mode in the demonstration grid. The functional and ICT architecture developed for the Portuguese Demonstrator of Évora is presented, focusing in the use cases defined to test and validate the tools developed to enable the active management of the LV grid during both normal and islanded modes.

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