António M. Lopes

A Remote Laboratory in Engineering Measurement

Online engineering practice is offering nowadays new potentials for training of measurement technologies and experimental procedures. In a laboratory mainly devoted to instrumentation for measurement by hands-on activity in engineering fields, students and engineering professionals are using, at present, online experiments in a blended-learning approach. A set of experiments has been designed and developed as well as some virtual simulators. The experiments integrated in a Moodle platform are using a Web-server system based on LabVIEW 7.1, linked to them by data acquisition interface cards, a video server, and a booking system developed as an extension of the Moodle platform. This paper reports a particular setup specially designed for remotely measuring and determining mechanical material properties and its combination with the design of a highly interactive user interface. The user may remotely conduct the experiment, getting numerical, graphical, and live video output information and receiving e-mailed experimental results.

Effect of Cure Temperature on the Glass Transition Temperature and Mechanical Properties of Epoxy Adhesives

This paper describes the influence of the curing temperature on the physical and mechanical properties of three structural adhesives. This work was undertaken to improve the understanding of the effect of curing temperature in the glass transition temperature, T g , and stiffness of epoxy adhesives. The mechanical properties (Youngs modulus and yield strength) of the adhesives were measured in bulk specimens. T g was measured by a dynamic mechanical analysis using an in-house developed apparatus. The curing process was the same for all tests, consisting of a curing stage followed by a post cure stage. The initial stage was performed at different temperatures. T g and the mechanical properties was found to vary as a function of the cure temperature of the adhesive. When cured below the cure temperature, T cure , at which the T g of the fully cured network, T g ∞, is achieved, the strength and stiffness of the adhesive increase as the cure temperature increases and the T g is higher than the cure temperature. When cured above the T cure at which the T g ∞ is achieved, the strength and stiffness decrease as the cure temperature increases and the T g is higher than the cure temperature.

Modelling and simulation of artificial locomotion systems

This paper describes a simulation model for a multi-legged locomotion system with joints at the legs having viscous friction, flexibility and backlash. For that objective the robot prescribed motion is characterized in terms of several locomotion variables. Moreover, the robot body is divided into several segments in order to emulate the behaviour of an animal spine. The foot-ground interaction is modelled through a non-linear spring-dashpot system whose parameters are extracted from the studies on soil mechanics. To conclude, the performance of the developed simulation model is evaluated through a set of experiments while the robot leg joints are controlled using fractional order algorithms.

Effect of post-cure on the glass transition temperature and mechanical properties of epoxy adhesives

The effects of post-curing and cure temperature on the glass transition temperature, T g, and the mechanical properties of epoxy adhesives were studied. T g was measured by a dynamic mechanical analysis apparatus developed in-house and the mechanical properties of the adhesives (yield strength, Young’s modulus and failure strain) were measured by a tensile machine. The relationships between T g and mechanical performance under various post-cure conditions were investigated. The curing process was the same for all tests, consisting of an initial stage performed at different temperatures followed by cooling at room temperature. Three sets of specimens were considered, sharing the same initial cure process, but with a different post-curing procedure. In the first set, the specimens were only subjected to a curing process; in the second set, the specimens were subjected to a curing process followed by a post-cure performed at a temperature below the T g of the fully cured network, T g∞; and in the third set, the specimens were subjected to a curing process followed by a post-cure performed at a temperature above the T g∞. When post-cured at a temperature above T g∞, the mechanical and physical properties tend to have a constant value for any cure temperature.

Analysis and Visualization of Seismic Data Using Mutual Information

Seismic data is difficult to analyze and classical mathematical tools reveal strong limitations in exposing hidden relationships between earthquakes. In this paper, we study earthquake phenomena in the perspective of complex systems. Global seismic data, covering the period from 1962 up to 2011 is analyzed. The events, characterized by their magnitude, geographic location and time of occurrence, are divided into groups, either according to the Flinn-Engdahl (F-E) seismic regions of Earth or using a rectangular grid based in latitude and longitude coordinates. Two methods of analysis are considered and compared in this study. In a first method, the distributions of magnitudes are approximated by Gutenberg-Richter (G-R) distributions and the parameters used to reveal the relationships among regions. In the second method, the mutual information is calculated and adopted as a measure of similarity between regions. In both cases, using clustering analysis, visualization maps are generated, providing an intuitive and useful representation of the complex relationships that are present among seismic data. Such relationships might not be perceived on classical geographic maps. Therefore, the generated charts are a valid alternative to other visualization tools, for understanding the global behavior of earthquakes.

Fractional order models of leaves

Leaves are mainly responsible for food production in vascular plants. Studying individual leaves can reveal important characteristics of the whole plant, namely its health condition, nutrient status, the presence of viruses and rooting ability. One technique that has been used for this purpose is Electrical Impedance Spectroscopy, which consists of determining the electrical impedance spectrum of the leaf. In this paper we use EIS and apply the tools of Fractional Calculus to model and characterize six species. Two modeling approaches are proposed: firstly, Resistance, Inductance, Capacitance electrical networks are used to approximate the leaves’ impedance spectra; afterwards, fractional-order transfer functions are considered. In both cases the model parameters can be correlated with physical characteristics of the leaves.

A RECOMBINANT ANTIGEN RECOGNIZED BY FASCIOLA HEPATICA–INFECTED HOSTS

This work reports the detection of specific immunoglobulins (Ig) against rFh8, a recombinant Fasciola hepatica adult worm excretion–secretion antigen, in sera from experimentally (rabbit, Wistar rat, cattle, and sheep), or naturally (human) infected hosts. In the case of laboratory experimental models the study revealed significant differences between rabbits, which recognized the recombinant antigen all along the infection, and Wistar rats, which showed high anti-rFh8 Ig levels only for a short period of the infection. Available sera from experimentally infected cattle and sheep, as well as sera from naturally F. hepatica–infected humans, also contained significant levels of Ig against rFh8, suggesting that Fh8 was produced by F. hepatica at a very early stage of infection in all hosts so far analyzed and that the rFh8 antigen could be used as a tool for the diagnosis of F. hepatica infections.

Design and implementation of a haptic‐based virtual assembly system

Purpose – Haptics can significantly enhance the users sense of immersion and interactivity. Especially in an assembly task, haptic feedback can help designers to have a better understanding of virtual objects and to increase task efficiency. The purpose of this paper is to investigate the design and implementation of a haptic‐based virtual assembly system (HVAS).Design/methodology/approach – A multi‐thread system structure was designed, an automatic data integration interface was developed to transfer geometry, topology, assembly and physics information from a computer‐aided design system to virtual reality application, and a hierarchical constraint‐based data model and scene graph structure was designed to construct the virtual assembly environment. Unlike traditional virtual assembly systems based on collision detection or geometry constraint only, a physics‐based modeling approach combining with haptic feedback and geometry constraint was undertaken to realize and guide the realistic assembly process....

Rhapsody in fractional

This paper studies several topics related with the concept of “fractional” that are not directly related with Fractional Calculus, but can help the reader in pursuit new research directions. We introduce the concept of non-integer positional number systems, fractional sums, fractional powers of a square matrix, tolerant computing and FracSets, negative probabilities, fractional delay discrete-time linear systems, and fractional Fourier transform.

Multidimensional Scaling Visualization Using Parametric Similarity Indices

In this paper, we apply multidimensional scaling (MDS) and parametric similarity indices (PSI) in the analysis of complex systems (CS). Each CS is viewed as a dynamical system, exhibiting an output time-series to be interpreted as a manifestation of its behavior. We start by adopting a sliding window to sample the original data into several consecutive time periods. Second, we define a given PSI for tracking pieces of data. We then compare the windows for different values of the parameter, and we generate the corresponding MDS maps of ‘points’. Third, we use Procrustes analysis to linearly transform the MDS charts for maximum superposition and to build a globalMDS map of “shapes”. This final plot captures the time evolution of the phenomena and is sensitive to the PSI adopted. The generalized correlation, theMinkowski distance and four entropy-based indices are tested. The proposed approach is applied to the Dow Jones Industrial Average stock market index and the Europe Brent Spot Price FOB time-series.