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UIDB/00066/2020 In this paper we introduce new discrete-time derivative concepts based on the bilinear (Tustin) transformation. From the new formulation, we obtain derivatives that exhibit a high degree of similarity with the continuous-time Grünwald-Letnikov derivatives. Their properties are described highlighting one important feature, namely that such derivatives have always long memory. publishersversion published

It has been shown that in reality at least two general scenarios of data structuring are possible: a a self-similar SS scenario when the measured data form an SS structure and b a quasi-periodic QP scenario when the repeated strongly correlated data form random sequences that are almost periodic with respect to each other. In the second case it becomes possible to describe their behavior and express a part of their randomness quantitatively in terms of the deterministic amplitude-frequency response belonging to the generalized Prony spectrum. This possibility allows us to re-examine the conventional concept of measurements and opens a new way for the description of a wide set of different data. In particular, it concerns different complex systems when the 'best-fit' model pretending to be the description of the data measured is absent but the barest necessity of description of these data in terms of the reduced number of quantitative parameters exists. The possibilities of the proposed approach and detection algorithm of the QP processes were demonstrated on actual data: spectroscopic data recorded for pure water and acoustic data for a test hole. The suggested methodology allows revising the accepted classification of different incommensurable and self-affine spatial structures and finding accurate interpretation of the generalized Prony spectroscopy that includes the Fourier spectroscopy as a partial case. © 2014 The Royal Swedish Academy of Sciences.

Catastrophic events, such as wars and terrorist attacks, tornadoes and hurricanes, earthquakes, tsunamis, floods and landslides, are always accompanied by a large number of casualties. The size distribution of these casualties has separately been shown to follow approximate power law (PL) distributions. In this paper, we analyze the statistical distributions of the number of victims of catastrophic phenomena, in particular, terrorism, and find double PL behavior. This means that the data sets are better approximated by two PLs instead of a single one. We plot the PL parameters, corresponding to several events, and observe an interesting pattern in the charts, where the lines that connect each pair of points defining the double PLs are almost parallel to each other. A complementary data analysis is performed by means of the computation of the entropy. The results reveal relationships hidden in the data that may trigger a future comprehensive explanation of this type of phenomena.

Submitted by Manuel Brandão (recipp@sc.ipp.pt) on 2016-04-11T08:37:56Z No. of bitstreams: 1 ART_MachadoTenreiro142_2012.pdf: 1003972 bytes, checksum: 47b9b7aca0d8d717f626d233f7afcb10 (MD5) Approved for entry into archive by Ana Rebelo (amsr@isep.ipp.pt) on 2019-03-26T11:49:24Z (GMT) No. of bitstreams: 1 ART_MachadoTenreiro142_2012.pdf: 1003972 bytes, checksum: 47b9b7aca0d8d717f626d233f7afcb10 (MD5) Made available in DSpace on 2019-03-26T11:49:25Z (GMT). No. of bitstreams: 1 ART_MachadoTenreiro142_2012.pdf: 1003972 bytes, checksum: 47b9b7aca0d8d717f626d233f7afcb10 (MD5) Previous issue date: 2012 N/A

Submitted by Manuel Brandão (recipp@sc.ipp.pt) on 2016-04-11T08:20:23Z No. of bitstreams: 1 ART_MachadoTenreiro151_2012.pdf: 328346 bytes, checksum: 5adf3e94c5998613eedbbd3be63f6bcb (MD5) Approved for entry into archive by Ana Rebelo (amsr@isep.ipp.pt) on 2019-03-26T11:40:46Z (GMT) No. of bitstreams: 1 ART_MachadoTenreiro151_2012.pdf: 328346 bytes, checksum: 5adf3e94c5998613eedbbd3be63f6bcb (MD5) Made available in DSpace on 2019-03-26T11:40:46Z (GMT). No. of bitstreams: 1 ART_MachadoTenreiro151_2012.pdf: 328346 bytes, checksum: 5adf3e94c5998613eedbbd3be63f6bcb (MD5) Previous issue date: 2012 N/A

In the last decades fractional calculus became an area of intense re-search and development. The accompanying poster illustrates the major contributions during the period 1966-2010., MSC 2010: 26A33, 05C72, 33E12, 34A08, 34K37, 35R11, 60G22

MSC 2010: 26A33, 05C72, 33E12, 34A08, 34K37, 35R11, 60G22, The fractional calculus (FC) is an area of intensive research and development. In a previous paper and poster we tried to exhibit its recent state, surveying the period of 1966-2010. The poster accompanying the present note illustrates the major contributions during the period 1695-1970, the "old history" of FC.

Submitted by Manuel Brandão (recipp@sc.ipp.pt) on 2016-04-11T10:18:45Z No. of bitstreams: 1 ART_MachadoTenreiro65_2008.pdf: 227062 bytes, checksum: 270bdef2f06a200684daacb021b14ba9 (MD5) Approved for entry into archive by Ana Rebelo (amsr@isep.ipp.pt) on 2019-03-26T14:58:27Z (GMT) No. of bitstreams: 1 ART_MachadoTenreiro65_2008.pdf: 227062 bytes, checksum: 270bdef2f06a200684daacb021b14ba9 (MD5) Made available in DSpace on 2019-03-26T14:58:27Z (GMT). No. of bitstreams: 1 ART_MachadoTenreiro65_2008.pdf: 227062 bytes, checksum: 270bdef2f06a200684daacb021b14ba9 (MD5) Previous issue date: 2008 info:eu-repo/semantics/publishedVersion

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Submitted by Manuel Brandão (recipp@sc.ipp.pt) on 2016-04-11T11:06:23Z No. of bitstreams: 1 ART_MachadoTenreiro57_2008.pdf: 1213623 bytes, checksum: 96f00adfd76d9e0d0a4816381ac2c13d (MD5) Approved for entry into archive by Ana Rebelo (amsr@isep.ipp.pt) on 2019-04-08T13:45:11Z (GMT) No. of bitstreams: 1 ART_MachadoTenreiro57_2008.pdf: 1213623 bytes, checksum: 96f00adfd76d9e0d0a4816381ac2c13d (MD5) Made available in DSpace on 2019-04-08T13:45:12Z (GMT). No. of bitstreams: 1 ART_MachadoTenreiro57_2008.pdf: 1213623 bytes, checksum: 96f00adfd76d9e0d0a4816381ac2c13d (MD5) Previous issue date: 2008 N/A

SUMMARYThis paper studies the mechanical configuration and the periodic gaits of multi-legged locomotion systems based on its kinematic and dynamic models. The purpose is to determine the system performance during walking, and the best set of locomotion variables that minimize a set of optimization indices. In this perspective, two kinematic and four dynamic indices are formulated to quantitatively measure the performance of the walking robot. The kinematic indices consist of the perturbation analysis and the locomobility measure, and the dynamic performance indices of the walking robot locomotion are the mean absolute density of energy, the mean power density dispersion, the density of power lost and the mean force at the body-legs interface. A set of model-based simulation experiments reveals the system configuration and the type of movements that lead to a better performance, for a specific locomotion mode, from the viewpoint of the proposed indices.

Submitted by Manuel Brandão (recipp@sc.ipp.pt) on 2016-04-11T11:37:41Z No. of bitstreams: 1 ART_MachadoTenreiro54_2007.pdf: 743875 bytes, checksum: 6553cc61895339cbba7a05b780f3f5ea (MD5) Approved for entry into archive by Ana Rebelo (amsr@isep.ipp.pt) on 2019-04-08T14:13:10Z (GMT) No. of bitstreams: 1 ART_MachadoTenreiro54_2007.pdf: 743875 bytes, checksum: 6553cc61895339cbba7a05b780f3f5ea (MD5) Made available in DSpace on 2019-04-08T14:13:10Z (GMT). No. of bitstreams: 1 ART_MachadoTenreiro54_2007.pdf: 743875 bytes, checksum: 6553cc61895339cbba7a05b780f3f5ea (MD5) Previous issue date: 2007 N/A

This paper is devoted to the synthesis of combinational logic circuits through computacional intelligence or, more precisely, using evolutionary algorithms, the Genetic and the memetic ALgorithm (GAs, MAs) and one swarm intelligence algorithm, the Particle Swarm Optimization (PSO). GAs are optimization and search techniques based on the principles os genetics and natural selection. MAs are evolutionary algorithms that include a stage of individual optimization as part of its search algorithm that starts with a population-based search algorithm that starts with a population of random solutions called particles. This paper presents the results for digital circuits design using the three above algorithms. The results show the statistical characteristics of this algorithms with respect to the number of generatons required to archieve the solutions. The article analyzes also a new fitness, function that includes an error discontinuity measure, which demonstrated to improved significantly the performance of the algorithm.

Submitted by Manuel Brandão (recipp@sc.ipp.pt) on 2016-04-11T12:00:25Z No. of bitstreams: 1 ART_MachadoTenreiro52_2007.pdf: 737184 bytes, checksum: 81391beaab29af8b47d6fcf7d41fd9e0 (MD5) Approved for entry into archive by Ana Rebelo (amsr@isep.ipp.pt) on 2019-04-08T14:53:47Z (GMT) No. of bitstreams: 1 ART_MachadoTenreiro52_2007.pdf: 737184 bytes, checksum: 81391beaab29af8b47d6fcf7d41fd9e0 (MD5) Made available in DSpace on 2019-04-08T14:53:47Z (GMT). No. of bitstreams: 1 ART_MachadoTenreiro52_2007.pdf: 737184 bytes, checksum: 81391beaab29af8b47d6fcf7d41fd9e0 (MD5) Previous issue date: 2007 N/A

Submitted by Manuel Brandão (recipp@sc.ipp.pt) on 2016-04-11T13:34:04Z No. of bitstreams: 1 ART_MachadoTenreiro42_2006.pdf: 771443 bytes, checksum: 1313005f7d5a7eefcd526211c0a09ebc (MD5) Approved for entry into archive by Ana Rebelo (amsr@isep.ipp.pt) on 2019-04-09T09:13:38Z (GMT) No. of bitstreams: 1 ART_MachadoTenreiro42_2006.pdf: 771443 bytes, checksum: 1313005f7d5a7eefcd526211c0a09ebc (MD5) Made available in DSpace on 2019-04-09T09:13:38Z (GMT). No. of bitstreams: 1 ART_MachadoTenreiro42_2006.pdf: 771443 bytes, checksum: 1313005f7d5a7eefcd526211c0a09ebc (MD5) Previous issue date: 2006-12 info:eu-repo/semantics/publishedVersion

Several Evolutionary Algorithms (EAs) are applied in the design and optimization of digital circuits, namely Genetic Algorithms (GAs), Memetic Algorithms (MAs) and swarm intelligence with Particle Swarm Optimization (PSO). GAs are optimization and search techniques based on the principles of genetics and natural selection. MAs are evolutionary algorithms that include a stage of individual optimization as part of its search strategy, being the individual optimization in the form of a local search. The combination of a global and a local search is a strategy used by many successful hybrid optimization approaches. PSO is a population-based search algorithm that starts with a population of random solutions called particles. In a PSO scheme each particle flies through the search space with a velocity that is adjusted dynamically according with its historical behavior. Therefore, the particles have a tendency to fly towards the best search area along the search process. In this line of thought, this paper presents the results for digital circuits design using the three above EAs.

In this paper we develop rational discrete-time approximations (IIR filters) to continuous fractional-order integrators and differentiators of type sα, α ∈ ℜ. For that, it is proposed the adoption of the techniques of Padé, Prony and Shanks usually applied in the signal modelling of deterministic signals. These methods yield suboptimal solutions to the problem which only requires finding the solution of a set of linear equations. The results reveal that this approach gives similar or superior approximations in comparison with other widely used methods. Their effectiveness is illustrated, both in the time and frequency domains, through several examples.

Mathematics Subject Classification: 26A33 (main), 35A22, 78A25, 93A30The generalization of the concept of derivative to non-integer values goes back to the beginning of the theory of differential calculus. Nevertheless, its application in physics and engineering remained unexplored up to the last two decades. Recent research motivated the establishment of strategies taking advantage of the Fractional Calculus (FC) in the modeling and control of many phenomena. In fact, many classical engineering applications deserve a closer attention and a new analysis in the viewpoint of FC. Bearing these ideas in mind, this work addresses the partial differential equations that model the electrical transmission lines. The distributed characteristics of this system may lead to design techniques, for integrated circuits, capable of implementing directly fractional-order impedances and, therefore, constitutes an alternative to exploring fractal geometries and dielectric properties.

In this paper, we present a new approach for tuning PID controllers. The proposed method is based on the application of basic fractional calculus concepts. In fact, the controller specifications include the desired gain crossover frequency and the slope at that frequency (which is equivalent to prescribing a specific phase margin) of a fractional-order integrator inserted in the forward path of unit feedback control system. The PID parameters are obtained by minimizing the integral of square error (ISE) between the step responses of the actual closed-loop system (with the fractional-order integrator) and that of the actual closed-loop system with the PID controller. The obtained closed-loop system is robust to gain variations with step responses exhibiting an iso-damping property. Simulation examples are given to illustrate the effectiveness and applicability of the proposed scheme.