Abstract

Abstract
Computer programming courses in higher education tend to have high rates of academic failure and students struggle, particularly so in the transition from entry-level programming to advanced programming. Some of the reasons given in the literature relate to the type of teaching approach and the strategies used by students and their attitudes towards computer programming. The literature also mentions that educational approaches are not always appropriate to the needs of students and to the development of skills required in the job market. We developed a teaching approach to try to address some of these issues and support students learning computer programming in the transition from entry-level to advanced computer programming: the SimProgramming approach. This approach was introduced at the University of Tros-os-Montes e Alto Douro (Portugal), within the scope of the course " Programming Methodologies III", part of the second curricular year of the programmes of studies in Informatics Engineering and in Information & Communication Technologies. We present in detail the origins of the SimProgramming approach, starting from the first trials that introduced, in two iterations, learning activities based on problem-based learning, and up to the third iteration where the current SimProgramming approach was implemented. We describe the reasoning, design and implementation of these three iterations, to show how the approach evolved. The SimProgramming approach is based in four conceptual foundations: business-like learning environment, self-regulated learning, co-regulated learning and formative assessment. For each of these conceptual foundations, we explain the teaching strategies adopted. In SimProgramming, the learning activity process develops in four phases, and students have specific tasks in each phase. We analyse interview data regarding student perceptions about the SimProgramming approach, and registration grids data on team work dynamics and final assessment of the assignment, noting the impact of SimProgramming in student grades. The application of SimProgramming revealed promising evidences in the overall results of student learning in the activities proposed in this approach. The average grades improved, and did the number of students regularly submitting their tasks on schedule. The perceptions of students regarding the SimProgramming approach are very positive: they recommend using it in the following years, and provided some suggestions to improve the approach. We conclude with reflections and recommendations for subsequent development of the SimProgramming approach in its application to the teaching of computer programming and potential for using it in other educational contexts.

Abstract
Optical fiber optrodes are attractive sensing devices due to their ability to perform point measurement in remote locations. Mostly, they are oriented to biochemical sensing, quite often supported by fluorescent and spectroscopic techniques, but with the refractometric approach considered as well when the objective is of high measurement performance, particularly when the focus is on enhancing the measurand resolution. In this work, we address this subject, proposing and analyzing the characteristics of a fiber optic optrode relying on plasmonic interaction. A linearly tapered optical fiber tip is covered by a double overlay: the inner one - a silver thin film and over it a dielectric layer, with this combination allowing to achieve, at a specific wavelength range, surface plasmonic resonance (SPR) interaction sensitive to the refractive index of the surrounding medium. Typically, the interrogation of the SPR sensing structures is performed, considering spectroscopic techniques, but in principle, a far better performance can be obtained, considering the reading of the phase of the light at a specific wavelength located within the spectral plasmonic resonance. This is the approach which is studied here in the context of the proposed optical fiber optrode configuration. The analysis performed shows the combination of a silver inner layer with a dielectric titanium oxide layer with tuned thicknesses enables sensitive phase reading and allows the operation of the fiber optic optrode sensor in the third telecommunication wavelength window.

Abstract
Achievable secrecy rates over a multiple-input multiple-output multipleeavesdropper (MIMOME) wiretap channel are considered, when the legitimate users have perfect knowledge only of the legitimate channel state and the eavesdropper channel is drawn from a (possibly unknown) continuous probability density. Legitimate users are assumed to deploy more antennas than the eavesdropper. A signaling transmission based on K-class Gaussian mixture model (GMM) distributions is proposed, which can be considered as an artificial-noise augmented signal, where the noise statistics are data-dependent. The proposed scheme is shown to achieve the secrecy capacity, log K, in the high signal-to-noise ratio (SNR) regime. Moreover, the tradeoff between secrecy and reliability at finite SNR is explored via the characterization of an upper bound to the error probability at the legitimate receiver, an upper bound to themutual information leakage to the eavesdropper and via numerical simulations. © Springer International Publishing Switzerland 2016.

Abstract
The constant growth of wind farms in the Brazilian electric system increases the concerns regarding power quality, especially related to harmonic distortions. At the same time, wind generation also becomes relevant in the context of power system stability, operating as ancillary services. One of the requirements of the system operator is the injection of reactive power by the wind farms to maintain the voltage levels. Considering that the actual studies only considers the operation of the wind generators with unitary power factor, the present work aims to evaluate the harmonic impact of Wind farms operating with reactive power injection on the electric system buses. For this purpose two monitoring campaigns in a wind farm of the CPFL Renováveis were performed with different power factors operating modes in the wind generators. These results were utilized in computational studies to evaluate the impact in voltage distortion at the PCC. The results obtained in this work demonstrated a significant impact on the harmonic current generation and in the voltage harmonic distortion due to the reactive power injection by the wind generators of the wind farm.

Abstract
Voltage source converter (VSC) can be considered as the heart of interfacing system for the integration of Distributed Generation (DG) sources into the power grid. Several control methods have been proposed for integration of DG sources into the power grid, and injection of high quality power. However, the converter-based DG interface is subjected to the unexpected uncertainties, which highly influence performance of control loop of DG unit and operation of interfaced converter. The interfacing impedance seen by interfaced VSC may considerably vary in power grid, and the stability of interfaced converter is highly sensitive to the impacts of this impedance changes; then, DG unit cannot inject appropriate currents. To deal with the instability problem, a control method based on fractional order active sliding mode is proposed in this paper, which is less sensitive to variations of interfacing impedance. A fractional sliding surface, which demonstrates the desired dynamics of system is developed and then, the controller is designed in two phases as sliding and reaching phases to keep the control loop stable. Stability issues of the control method are discussed in details and the conditions in which the proposed model works in a stable operating mode is defined. The proposed control method takes a role to provide high quality power injection and ensures precise references tracking and fast response despite such uncertainties. Theoretical analyses and simulation results are established to confirm the performance and feasibility of the proposed control method in DG technology.