Robotic manipulators with vibrations: short time fourier transform of fractional spectra

This paper analyzes the signals captured during impacts and vibrations of a mechanical manipulator. In order to acquire and study the signals an experimental setup is implemented. The signals are treated through signal processing tools such as the fast Fourier transform and the short time Fourier transform. The results show that the Fourier spectrum of several signals presents a non integer behavior. The experimental study provides valuable results that can assist in the design of a control system to deal with the unwanted effects of vibrations.

Complex-order dynamics in hexapod locomotion

This paper studies the dynamics of foot–ground interaction in hexapod locomotion systems. For that objective the robot motion is characterized in terms of several locomotion variables and the ground is modelled through a non-linear spring-dashpot system, with parameters based on the studies of soil mechanics. Moreover, it is adopted an algorithm with foot-force feedback to control the robot locomotion. A set of model-based experiments reveals the influence of the locomotion velocity on the foot–ground transfer function, which presents complex-order dynamics.

Dynamical modelling of a genetic algorithm

This work addresses the signal propagation and the fractional-order dynamics during the evolution of a genetic algorithm (GA). In order to investigate the phenomena involved in the GA population evolution, the mutation is exposed to excitation perturbations during some generations and the corresponding fitness variations are evaluated. Three distinct fitness functions are used to study their influence in the GA dynamics. The input and output signals are studied revealing a fractional-order dynamic evolution, characteristic of a long-term system memory.

Fractional order electromagnetics

The Maxwell equations constitute a formalism for the development of models describing electromagnetic phenomena. The four Maxwell laws have been adopted successfully in many applications and involve only the integer order differential calculus. Recently, a closer look for the cases of transmission lines, electrical motors and transformers, that reveal the so-called skin effect, motivated a new perspective towards the replacement of classical models by fractional-order mathematical descriptions. Bearing these facts in mind this paper addresses the concept of static fractional electric potential. The fractional potential was suggested some years ago. However, the idea was not fully explored and practical methods of implementation were not proposed. In this line of thought, this paper develops a new approximation algorithm for establishing the fractional order electrical potential and analyzes its characteristics.

Time domain design of fractional differintegrators using least-squares

In this paper we propose the use of the least-squares based methods for obtaining digital rational approximations (IIR filters) to fractional-order integrators and differentiators of type sα, α∈R. Adoption of the Padé, Prony and Shanks techniques is suggested. These techniques are usually applied in the signal modeling 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 the least-squares approach gives similar or superior approximations in comparison with other widely used methods. Their effectiveness is illustrated, both in the time and frequency domains, as well in the fractional differintegration of some standard time domain functions.

Which differintegration?

Despite the great advances in the theory and applications of fractional calculus, some topics remain unclear, making a systematic use difficult. In this paper, the fractional differintegration definition problem is studied from a systems point of view. Both local (Grunwald-Letnikov) and global (convolutional) definitions are considered. It is shown that the Cauchy formulation should be adopted since it is coherent with usual practice in signal processing and control applications.

Uso de Interfaces Cérebro-computador na comunicação de pessoas com Síndrome de Encarceramento

Os avanços nas Interfaces Cérebro-máquina, resultantes dos avanços no tratamento de sinal e da inteligência artificial, estão a permitir-nos aceder à atividade cerebral, descodificá-la, e usála para comandar dispositivos, sejam eles braços artificiais ou computadores. Isto é muito mais importante quando os utilizadores são pessoas que perderam a capacidade de comunicar, embora mantenham as suas capacidades cognitivas intactas. O caso mais extremo desta situação é o das pessoas afetadas pela Síndrome de Encarceramento. Este trabalho pretende contribuir para a melhoria da qualidade de vida das pessoas afetadas por esta síndrome, disponibilizando-lhes um meio de comunicação adaptado às suas limitações. É essencialmente um estudo de usabilidade aplicada a um tipo de utilizador extremamente diminuído na sua capacidade de interação. Nesta investigação começamos por compreender a Síndrome de Encarceramento e as limitações e capacidades das pessoas afetadas por ela. Abordamos a neuroplasticidade, o que é, e em que medida é importante para a utilização das Interfaces Cérebro-máquina. Analisamos o funcionamento destas interfaces, e os fundamentos científicos que o suportam. Finalmente, com todo este conhecimento em mãos, investigamos e desenvolvemos métodos que nos permitissem otimizar as limitadas capacidades do utilizador na sua interação com o sistema, minimizando o esforço e maximizando o desempenho. Foi para o efeito desenhado e implementado um protótipo que nos permitisse validar as soluções encontradas.

Análise e implementação de filtros digitais fraccionários

O projeto realizado teve como tema a aplicação das derivadas e integrais fraccionários para a implementação de filtros digitais numa perspetiva de processamento digital de sinais. Numa primeira fase do trabalho, é efetuado uma abordagem teórica sobre os filtros digitais e o cálculo fraccionário. Estes conceitos teóricos são utilizados posteriormente para o desenvolvimento do presente projeto. Numa segunda fase, é desenvolvida uma interface gráfica em ambiente MatLab, utilizando a ferramenta GUIDE. Esta interface gráfica tem como objetivo a implementação de filtros digitais fraccionários. Na terceira fase deste projeto são implementados os filtros desenvolvidos experimentalmente através do ADSP-2181, onde será possível analisar e comparar os resultados experimentais com os resultados obtidos por simulação no MatLab. Como quarta e última fase deste projeto é efetuado uma reflexão sobre todo o desenvolvimento da Tese e o que esta me proporcionou. Com este relatório pretendo apresentar todo o esforço aplicado na realização deste trabalho, bem como alguns dos conhecimentos adquiridos ao longo do curso.

A Random Access Protocol incorporating Multi-Packet Reception, Retransmission Diversity and Successive Interference Cancellation

8th International Workshop on Multiple Access Communications (MACOM2015), Helsinki, Finland.

A Review on the Characterization of Signals and Systems by Power Law Distributions

Power laws, also known as Pareto-like laws or Zipf-like laws, are commonly used to explain a variety of real world distinct phenomena, often described merely by the produced signals. In this paper, we study twelve cases, namely worldwide technological accidents, the annual revenue of America׳s largest private companies, the number of inhabitants in America׳s largest cities, the magnitude of earthquakes with minimum moment magnitude equal to 4, the total burned area in forest fires occurred in Portugal, the net worth of the richer people in America, the frequency of occurrence of words in the novel Ulysses, by James Joyce, the total number of deaths in worldwide terrorist attacks, the number of linking root domains of the top internet domains, the number of linking root domains of the top internet pages, the total number of human victims of tornadoes occurred in the U.S., and the number of inhabitants in the 60 most populated countries. The results demonstrate the emergence of statistical characteristics, very close to a power law behavior. Furthermore, the parametric characterization reveals complex relationships present at higher level of description.

Fractional order describing functions

This paper addresses limit cycles and signal propagation in dynamical systems with backlash. The study follows the describing function (DF) method for approximate analysis of nonlinearities and generalizes it in the perspective of the fractional calculus. The concept of fractional order describing function (FDF) is illustrated and the results for several numerical experiments are analysed. FDF leads to a novel viewpoint for limit cycle signal propagation as time-space waves within system structure.

Integer/fractional decomposition of the impulse response of fractional linear systems

The decomposition of a fractional linear system is discussed in this paper. It is shown that it can be decomposed into an integer order part, corresponding to possible existing poles, and a fractional part. The first and second parts are responsible for the short and long memory behaviors of the system, respectively, known as characteristic of fractional systems.

Fractional Order Description of DNA

This study addresses the deoxyribonucleic acid (DNA) and proposes a procedure based on the association of statistics, information theory, signal processing, Fourier analysis and fractional calculus for describing fundamental characteristics of the DNA. In a first phase the 24 chromosomes of the Human are evaluated. In a second phase, 10 chromosomes for different species are also processed and the results compared. The results reveal invariance in the description and close resemblances with fractional Brownian motion.

Fractional Analysis of the DNA Information

Proceedings of the 12th Conference on 'Dynamical Systems -Theory and Applications'

Towards a classification scheme for musical sounds

Signal Processing: Algorithms, Architectures, Arrangements, and Applications (SPA), 2013