Manuel J. C. S. Reis

Construction of Aharonov-Berry's superoscillations

A simple method is described for constructing functions that superoscillate at an arbitrarily chosen wavelength scale. Our method is based on the technique of oversampled signal reconstruction. This allows us to explicitly demonstrate that the observed fragility of superoscillating wavefunctions is indeed mathematically closely connected to what in the communication theory community is known as the instability of oversampled signal reconstruction, confirming a previous conjecture. This is of potential interest, for example, concerning the understanding of the practical difficulties in experimentally producing superoscillatory wavefunctions.

Induction motor response to periodical voltage fluctuations

The main aim of this paper is to analyze the behavior of the three-phase squirrel cage induction motor under different voltage fluctuation levels. To achieve this goal several simulations were performed using the EMTP/ATP tool. Here we present how mechanical torque, speed and efficiency parameters varied with different levels of voltage fluctuation and modeling frequencies. As it was expected, the induction motor is sensitive to voltage fluctuations within certain amplitude levels and frequencies. Also, the speed is more affected by low frequencies and high amplitudes of voltage fluctuations, while the torque and efficiency are more affected by middle and high frequencies and amplitudes.

A Windows‐based software package to evaluate residual stresses by the incremental hole‐drilling technique

A new software package for the incremental hole‐drilling technique (IHD) is presented in connection with undergraduate mechanical engineering education. The main available technical residual stresses evaluation procedures for applying IHD in isotropic materials are reviewed and have been included in the package. It has an easy‐to‐use, friendly interface, and can be used as a tool to teach the IHD technique or as a laboratory to study its applicability to real world problems. A set of exercises have been prepared, which are freely distributed to our students, in order to show the full potential of the package, but the students can also do simulations and experiments with their own data.

Instrumented hip joint replacements, femoral replacements and femoral fracture stabilizers

This paper reviews instrumented hip joint replacements, instrumented femoral replacements and instrumented femoral fracture stabilizers. Examination of the evolution of such implants was carried out, including the detailed analysis of 16 architectures, designed by 8 research teams and implanted in 32 patients. Their power supply, measurement, communication, processing and actuation systems were reviewed, as were the tests carried out to evaluate their performance and safety. These instrumented implants were only designed to measure biomechanical and thermodynamic quantities in vivo, in order to use such data to conduct research projects and optimize rehabilitation processes. The most promising trend is to minimize aseptic loosening and/or infection following hip or femoral replacements or femoral stabilization procedures by using therapeutic actuators inside instrumented implants to apply controlled stimuli in the bone–implant interface.

VoIP reconstruction under a minimum interpolation algorithm

This paper describes a linear interpolation algorithm and compares it with the discrete Papoulis-Gerchberg applied to voice signal reconstruction. The simulation results, measured as reconstruction time and signal accuracy, show that such method achieves good results. By combining the proposed algorithm with a proper packetisation scheme, it may be useful in VoIP communications.

Linear combinations of B-splines as generating functions for signal approximation

The advantages of B-splines for signal representation are well known. This paper explores a fact that seems to be less well known, namely, the possibility of using linear combinations of B-splines to obtain representations that are more stable than the usual ones. We give the best possible Riesz bounds for these linear combinations and calculate their duals, in a generalized sampling context.

Signal and Image Reconstruction in Undergraduate Education: Tools for Assessing and Comparing a Set of Algorithms

This paper discusses signal and image reconstruction in connection with undergraduate electrical engineering education. It briefly reviews some of the basic signal and image reconstruction techniques, and presents two Java applets that have been found useful in the context. The applets have easy‐to‐use, friendly interfaces, and can be used as tools to teach reconstruction techniques or as a laboratory to study the applicability of the methods to real world signals and images. The students can do simulations with their own data (signals or images) on any computer platform.

HarmoSim: A tool for harmonic distortion simulation and assessment of nonlinear loads

Electrical power quality (PQ) is a crucial competitive and developing factor to all economic activities. The economic impact resulting from a bad PQ would be drastic on all consumers. Computers, uninterruptible and switched power supplies (UPS), and fluorescent lamps/tubes are examples of nonlinear loads that have the consumption of a nonsinusoidal current, which cause disturbances in the power supply system (that may be severe or not). This study discusses residential generic power circuitry analysis and simulation, under nonlinear loads, in connection with undergraduate electrical engineering education. It briefly reviews some of the basic techniques, and presents a software tool that has been found to be very useful in the context. The tool has an easy‐to‐use, friendly interface, and can be used to teach design techniques or as a laboratory support to study the applicability of known methods to real situations. The students can perform simulations with their own data on Microsoft™ Windows®‐based platforms.

Automatic Detection of White Grapes in Natural Environment Using Image Processing

The rate of adoption of Precision Agriculture and Precision Viticulture production systems in the Douro Demarcated Region remains low. We believe that one way to raise it is to address challenging real-world problems whose solution offers a clear benefit to the viticulturist. For example, one of the most demanding tasks in wine making is harvesting. Even for humans, the detection of grapes in their natural environment is not always easy. White grapes are particularly difficult to detect, since their color is similar to that of the leafs. Here we present a low cost system for the detection of white grapes in natural environment color images. The system also calculates the probable location of the bunch stem and achieves 91% of correct classifications.

3D Map and DGPS Validation for a Vineyard Autonomous Navigation System

An autonomous DGPS navigation system must use an accurate threedimensional (3D) digital map. However, it is crucial to validate it using data collected in the field. One possible way to validate the map is to employ a vehicle driven by an expert to ensure that the trajectory is plotted within the boundaries of navigation paths. It is essential to take this care, especially when the terrain is very highly uneven and small differences in position may correspond to large vertical deviations. A small navigation error can result in a serious fall, which may damage or even destroy the vehicle. In the Douro Demarcated Region, in northern Portugal, the vineyard is planted on narrow terraces built on steep hills along the winding Douro River. This paper presents the results of a dynamic trajectory survey obtained from a real navigation procedure, carried out by an expert driving an instrumented tractor during the spraying of the vineyard. The results were obtained using a DGPS (accuracy = 2 cm) and compared to an existing Digital Elevation Model (DEM) of the vineyard already created by the authors’ work group, with an average accuracy of 10 cm. The results are shown in a C# developed interface with OpenGL facilities, which enable the viewing of the 3D vineyard details. The results confirm the validation of the methodology previously adopted for map extraction and respective equipment selection. The trajectory of the tractor, including some maneuvers, is drawn within the inner and outer edges of each terrace or path that exists in the vineyard. The interface can also be used as an important tool in path planning to automatically extract the topology of the vineyard and to select the best path to carry out some vineyard tasks.