Signal generator based on a chaotic circuit

"This paper is about a signal generator based on Chua´s circuit. It is able to generate chaotic and sinusoidal signals. It can generate other types of waveforms as well. These results are seen in the experiment carried out on the signal generator. Simple hardware like operational amplifiers along with passive components such as resistors and capacitors are used to make the signal generator.

Difference map and its electronic circuit realization

"In this paper we study the dynamical behavior of the one-dimensional discrete-time system, the so-called iterated map. Namely, a bimodal quadratic map is introduced which is obtained as an amplification of the difference between well-known logistic and tent maps. Thus, it is denoted as the so-called difference map. The difference map exhibits a variety of behaviors according to the selection of the bifurcation parameter. The corresponding bifurcations are studied by numerical simulations and experimentally. The stability of the difference map is studied by means of Lyapunov exponent and is proved to be chaotic according to Devaney’s definition of chaos. Later on, a design of the electronic implementation of the difference map is presented. The difference map electronic circuit is built using operational amplifiers, resistors and an analog multiplier. It turns out that this electronic circuit presents fixed points, periodicity, chaos and intermittency that match with high accuracy to the corresponding values predicted theoretically.

Forced synchronization of autonomous dynamical Boolean networks

"We present the design of an autonomous time-delay Boolean network realized with readily available electronic components. Through simulations and experiments that account for the detailed nonlinear response of each circuit element, we demonstrate that a network with five Boolean nodes displays complex behavior. Furthermore, we show that the dynamics of two identical networks display near-instantaneous synchronization to a periodic state when forced by a common periodic Boolean signal. A theoretical analysis of the network reveals the conditions under which complex behavior is expected in an individual network and the occurrence of synchronization in the forced networks. This research will enable future experiments on autonomous time-delay networks using readily available electronic components with dynamics on a slow enough time-scale so that inexpensive data collection systems can faithfully record the dynamics.

Class imbalance impact on the prediction of complications during home hospitalization: a comparative study.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksHome hospitalization (HH) is presented as a healthcare alternative capable of providing high standards of care when patients no longer need hospital facilities. Although HH seems to lower healthcare costs by shortening hospital stays and improving patient's quality of life, the lack of continuous observation at home may lead to complications in some patients. Since blood tests have been proven to provide relevant prognosis information in many diseases, this paper analyzes the impact of different sampling methods on the prediction of HH outcomes. After a first exploratory analysis, some variables extracted from routine blood tests performed at the moment of HH admission, such as hemoglobin, lymphocytes or creatinine, were found to unmask statistically significant differences between patients undergoing successful and unsucessful HH stays. Then, predictive models were built with these data, in order to identify unsuccessful cases eventually needing hospital facilities. However, since these hospital admissions during HH programs are rare, their identification through conventional machine-learning approaches is challenging. Thus, several sampling strategies designed to face class imbalance were herein overviewed and compared. Among the analyzed approaches, over-sampling strategies, such as ROSE (Random Over-Sampling Examples) and conventional random over-sampling, showed the best performances. Nevertheless, further improvements should be proposed in the future so as to better identify those patients not benefiting from HHPeer ReviewedPostprint (author's final draft

Set-reset flip-flop circuit with a simple output logic

"The equation of the plane (EOP) in analytic geometry is used to build a logic dynamic architecture, i.e., a combination of set-reset flip-flop (SR-FF) and basic logic gates. This is achieved by using two of the variables in the EOP as the input signals of the SR-FF and the remaining variable as the output signal. This theoretical proposal for mixing the SR-FF and the basic logic gates is confirmed experimentally by means of a simple electronic implementation.

Fourier series expansion for nonlinear Hamiltonian oscillators

The problem of nonlinear Hamiltonian oscillators is one of the classical questions in physics. When an analytic solution is not possible, one can resort to obtaining a numerical solution or using perturbation theory around the linear problem. We apply the Fourier series expansion to find approximate solutions to the oscillator position as a function of time as well as the period-amplitude relationship. We compare our results with other recent approaches such as variational methods or heuristic approximations, in particular the Ren-He's method. Based on its application to the Duffing oscillator, the nonlinear pendulum and the eardrum equation, it is shown that the Fourier series expansion method is the most accurate

Chua´s circuit and its characterization as a filter

"This article deals with Chuaʼs circuit characterization from the point of view of a filter based on the concept of piecewise linear functions. Furthermore, experiments are developed for teaching electronic systems that can be used for novel filtering concepts. The frequency range in which they are tested is from $20\;{\rm Hz}$ to $20\;{\rm kHz}$, due to the audio spectrum comprised in this frequency range. The node associated with the capacitor and Chuaʼs diode is used as input, and the node for another capacitor and the coil is used as output, thereby establishing one input–output relationship for each system case given by the piecewise linear functions. The experimental result shows that Chuaʼs circuit behaves as a bandpass filter-amplifier, with a maximum frequency around $3\;{\rm kHz}$ and bandwidth between $1.5\;{\rm kHz}$ and $5.5\;{\rm kHz}$. The results presented in this paper can motivate engineering students to pursue applications of novel electrical circuits based on topics that are of potential interest in their future research studies.

Aterramento do ponto neutro das redes de distribuição através de bobina ressonante.

O assunto principal desta dissertação é o método de aterramento do ponto neutro utilizado nas redes de distribuição de energia elétrica. Realiza-se um estudo dos diversos métodos de aterramento utilizados no mundo e os mais utilizados no Brasil, procurando analisar as vantagens e desvantagens de cada método para assim propor um método de aterramento que seja mais eficiente, ou seja, que possibilite o menor número de interrupções relacionadas a defeitos que envolvam a “Terra”. Para melhor compreensão da função do sistema de aterramento em um sistema elétrico de distribuição de energia dedica-se um capítulo para descrição do sistema elétrico de distribuição, ressaltando suas principais características e funcionalidade. Com o mesmo intuito, descreve-se também os principais tipos de falhas que ocorrem no sistema de distribuição, principalmente as que envolvam a “Terra, para que se possa determinar o método de aterramento a ser utilizado. Com base nos estudos e análises realizados, propõem-se o método de aterramento que utiliza uma bobina ressonante com a impedância capacitiva do sistema elétrico, conhecida como “Bobina de Petersen”, em homenagem a seu inventor. Essa bobina tem como função principal limitar a corrente de defeito fase-terra e agir na eliminação do arco de defeito e consequentemente a falha, impedindo o desligamento do sistema. Realizam-se vários estudos e simulações para verificação da viabilidade da aplicação deste método de aterramento em um sistema real de distribuição de energia elétrica

Da teoria à prática em contexto escolar

O Teorema do Limite Central garante que o único modelo estável para somas com variância finita é o modelo normal. Esta noção de estabilidade tornou mais fácil a modelação de fenômenos aditivos, uma vez que a acumulação de informação, sob a forma de mais parcelas, apenas nos faz mudar a localização e a escala, mas permanecemos no mesmo modelo. Contudo, a convergência de somas para uma normal dá-se quando nenhuma das parcelas tem um papel preponderante, ou seja, quando as caudas da distribuição subjacente tem um peso moderado, que é explicitado através da exigência da existência de segundo momento. Esta situação altera-se quando as estatísticas ordinais extremais têm algum protagonismo, o que acontece se o modelo distribucional de base tiver caudas pesadas. Neste trabalho investigamos o comportamento distribucional de somas e de estatísticas ordinais extremais, em particular do máximo. Obtemos a distribuição exata de algumas somas de variáveis aleatórias reais independentes e do máximos de variáveis aleatórias independentes e identicamente distribuídas. Analisamos o comportamento assintótico das estatísticas ordinais centrais, regido pelo Teorema do Limite Central, e das estatísticas ordinais extremais, nomeadamente do máximo, regido pelo Teorema Limite Extremal. Enquadramos alguns dos assuntos abordados, como a média amostral e as distribuições amostrais, no ensino, com a análise das dificuldades dos alunos nestes temas e a análise dos programas de Matemática do ensino secundário e de uma unidade curricular de um curso de formação de professores de Matemática em Angola.The Central Limit Theorem guarantees that the only stable model for sums with finite variance is the normal model. This notion of stability has made it easier to model additive phenomena, since accumulating information in the form of more terms only makes us change the location and the scale, but we remain in the same model. However, the convergence of sums to a normal distribution occurs when no terms have a preponderant role, in other words, when the tails of the underlying distribution have a moderate weight, which is explained by the requirement of the existence of second moment. This situation changes when extreme ordinal statistics play a key role, which happens if the underlying distributional model is heavy tailed. In this work we investigate the distributional behavior of sums and extreme ordinal statistics, maximum in particular. We obtain the exact distribution of some sums of independent real random variables and independent and of maximum of identically distributed random variables. We analyze the asymptotic behavior of central ordinal statistics, governed by the Central Limit Theorem, and the extremal ordinal statistics, namely maximum, governed by the Extremal Types Theorem. We put into teaching context some of the subjects discussed, such as the sample mean and sampling distributions, by analyzing students difficulties in these subjects and the Mathematic programs of secondary school and a curricular unit of a teacher training course of Mathematics in Angola

Sobredimensionamiento en la selección de motores de inducción: aspectos técnicos y económicos

El desconocimiento a la hora de la elección de un motor de inducción puede acarrear una pérdida económica y un mal uso de la energía. En este proyecto se abordan las ventajas e inconvenientes que puede tener utilizar un motor con mayor potencia a la potencia demandada. Para ello, se ha estructurado el proyecto en dos partes: una parte más tecnológica o de ingeniería y otra parte económica. Dentro de la parte ingenieril, se ha tratado el estudio teórico de los motores, la utilización y el entendimiento de catálogos, así como, el análisis de gráficas y de posibles cambios en el futuro, es decir, análisis de sensibilidad. La parte económica, también ha sido de gran importancia en este proyecto debido a que la finalidad de éste es averiguar la mayor rentabilidad dentro de una serie de situaciones diferentes. Para estos análisis de rentabilidad se han utilizado indicadores como el valor actualizado neto (VAN), la tasa interna de retorno (TIR) y el pay back (PB). Además, se ha estudiado una hipotética situación, en la cual se produciría un cambio de motor a uno más eficiente, repercutiendo tanto en una nueva inversión, como en una menor cantidad de energía consumida (mejora de la eficiencia del sistema).The lack of knowledge at the time of choosing an induction motor can result in a loss of money. This project addresses the advantages and disadvantages that can be used to use a motor with more power to the power demanded. For this, the project has been structured in two parts: an engineering part and an economic part. Within the engineering part, the theoretical study of motors, the use and understanding of catalogs, as well as the analysis of graphs and possible changes in the future, that is, sensitivity analysis, have been discussed. The economic part, has also been of great importance in this project because the purpose of this is to find out the highest profitability within a series of different situations. For these profitability analyzes, indicators such as NPV, IRR and PB have been used. In addition, a hypothetical situation has been studied, in which there would be a change of engine to a more efficient, impacting both a new investment, and a lower energy consumption.Universidad de Sevilla. Grado en Ingeniería de la Energí