Generalized Wave Digital Filter Realizations of Arbitrary Reciprocal Connection Networks

In this paper, an existing approach for modeling and efficiently implementing arbitrary reciprocal connection networks using wave digital (WD) scattering junctions based on voltage waves is extended to be used in a broader class of WD filters (WDFs) based on different kinds of waves. A generalized wave definition which includes traditional voltage waves, current waves, and power-normalized waves as particular cases is employed. Closed-form formulas for computing the scattering matrices of the junctions are provided. Moreover, the approach is also extended to the family of Biparametric WDFs, which have been recently introduced in the literature

advances in wave digital modeling of linear and nonlinear systems a summary

This brief summarizes some of the main research results that I obtained during the three years, ranging from November 2015 to October 2018, as a Ph.D. student at Politecnico di Milano under the supervision of Professor Augusto Sarti, and that are contained in my doctoral dissertation, entitled "Advances in Wave Digital Modeling of Linear and Nonlinear Systems". The thesis provides contributions to all the main aspects of Wave Digital (WD) modeling of lumped systems: it introduces generalized definitions of wave variables; it presents novel WD models of one- and multi-port linear and nonlinear circuit elements; it discusses systematic techniques for the WD implementation of arbitrary connection networks and it describes a novel iterative method for the implementation of circuits with multiple nonlinear elements. Though WD methods usually focus on the discrete-time implementation of analog audio circuits; the methodologies addressed in the thesis are general enough as to be applicable to whatever system that can be described by an equivalent electric circuit

Decoding the spectra of SDSS early-type galaxies: New indicators of age and recent star formation

(Abridged) We apply Principal Component Analysis (PCA) to a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS) in order to infer differences in their star formation histories. Out of the first few principal components (PC), we study four which give information about stellar populations and velocity dispersion. We construct two parameters (eta and zeta) as linear combinations of PC1 and PC2. We find zeta to be most sensitive to recent episodes of star formation, and eta to be strongly dependent on the average age of the stellar populations. The distribution of the eta component of the composites appear to be indistinguishable between high and low density regions, whereas the distribution of zeta parameters have a significant skew towards lower values for galaxies in low density regions. This result suggests that galaxies in lower density environments are less likely to present weak episodes of recent star formation. In contrast, a significant number of galaxies from our high density subsample -- which includes clusters (both outer regions and centres) and groups -- underwent small but detectable recent star formation at high metallicity, in agreement with recent estimates targeting elliptical galaxies in Hickson Compact Groups and in the field (Ferreras et al.).Comment: 19 pages, 12 figures. Accepted for publication in MNRA

Deep Learning-Based Wave Digital Modeling of Rate-Dependent Hysteretic Nonlinearities for Virtual Analog Applications

Electromagnetic components greatly contribute to the peculiar timbre of analog audio gear. Indeed, distortion effects due to the nonlinear behavior of magnetic materials are known to play an important role in enriching the harmonic content of an audio signal. However, despite the abundant research that has been devoted to the characterization of nonlinearities in the context of virtual analog modeling over the years, the discrete-time simulation of circuits exhibiting rate-dependent hysteretic phenomena remains an open challenge. In this article, we present a novel data-driven approach for the wave digital modeling of rate-dependent hysteresis using recurrent neural networks (RNNs). Thanks to the modularity of wave digital filters, we are able to locally characterize the wave scattering relations of a hysteretic reluctance by encapsulating an RNN-based model into a single one-port wave digital block. Hence, we successfully apply the proposed methodology to the emulation of the output stage of a vacuum-tube guitar amplifier featuring a nonlinear transformer

Canonical Piecewise-Linear Representation of Curves in the Wave Digital Domain

Global, explicit representations of nonlinearities are desirable when implementing nonlinear Wave Digital (WD) structures, as they free us from the burden of managing look-up tables, performing data interpolation and/or using iterative solvers. In this paper we present a method that, starting from certain parameterized PieceWise-Linear (PWL) curves in the Kirchhoff domain, allows us to express them in the WD domain using a global and explicit representation. We will show how some curves (multi-valued functions in the Kirchhoff domain) can be represented as functions in canonical PWL form in the WD domain. In particular, we will present a procedure, which, in the most general case, also returns the conditions on the reference port resistance under which it is possible to find explicit mappings in the WD domain

Development of an active vision system for robot inspection of complex objects

Dissertação de mestrado integrado em Engenharia Mecânica (área de especialização em Sistemas Mecatrónicos)The dissertation presented here is in the scope of the IntVis4Insp project between University of Minho and the company Neadvance. It focuses on the development of a 3D hand tracking system that must be capable of extracting the hand position and orientation to prepare a manipulator for automatic inspection of leather pieces. This work starts with a literature review about the two main methods for collecting the necessary data to perform 3D hand tracking. These divide into glove-based methods and vision-based methods. The first ones work with some kind of support mounted on the hand that holds all the necessary sensors to measure the desired parameters. While the second ones recur to one or more cameras to capture the hands and through computer vision algorithms track their position and configuration. The selected method for this work was the vision-based method Openpose. For each recorded image, this application can locate 21 hand keypoints on each hand that together form a skeleton of the hands. This application is used in the tracking system developed throughout this dissertation. Its information is used in a more complete pipeline where the location of those hand keypoints is crucial to track the hands in videos of the demonstrated movements. These videos were recorded with an RGB-D camera, the Microsoft Kinect, which provides a depth value for every RGB pixel recorded. With the depth information and the 2D location of the hand keypoints in the images, it was possible to obtain the 3D world coordinates of these points considering the pinhole camera model. To define the hand, position a point is selected among the 21 for each hand, but for the hand orientation, it was necessary to develop an auxiliary method called “Iterative Pose Estimation Method” (ITP), which estimates the complete 3D pose of the hands. This method recurs only to the 2D locations of every hand keypoint, and the complete 3D world coordinates of the wrists to estimate the right 3D world coordinates of all the remaining points on the hand. This solution solves the problems related to hand occlusions that a prone to happen due to the use of only one camera to record the inspection videos. Once the world location of all the points in the hands is accurately estimated, their orientation can be defined by selecting three points forming a plane.A dissertação aqui apresentada insere-se no âmbito do projeto IntVis4Insp entre a Universidade do Minho e a empresa Neadavance, e foca-se no desenvolvimento de um sistema para extração da posição e orientação das mãos no espaço para posterior auxílio na manipulação automática de peças de couro, com recurso a manipuladores robóticos. O trabalho inicia-se com uma revisão literária sobre os dois principais métodos existentes para efetuar a recolha de dados necessária à monitorização da posição e orientação das mãos ao longo do tempo. Estes dividem-se em métodos baseados em luvas ou visão. No caso dos primeiros, estes recorrem normalmente a algum tipo de suporte montado na mão (ex.: luva em tecido), onde estão instalados todos os sensores necessários para a medição dos parâmetros desejados. Relativamente a sistemas de visão estes recorrem a uma câmara ou conjunto delas para capturar as mãos e por via de algoritmos de visão por computador determinam a sua posição e configuração. Foi selecionado para este trabalho um algoritmo de visão por computador denominado por Openpose. Este é capaz de, em cada imagem gravada e para cada mão, localizar 21 pontos pertencentes ao seu esqueleto. Esta aplicação é inserida no sistema de monitorização desenvolvido, sendo utilizada a sua informação numa arquitetura mais completa onde é efetuada a extração da localização dos pontos chave de cada mão nos vídeos de demonstração dos movimentos de inspeção. A gravação destes vídeos é efetuada com uma câmara RGB-D, a Microsoft Kinect, que fornece um valor de profundidade para cada pixel RGB gravado. Com os dados de profundidade e a localização dos pontos chave nas imagens foi possível obter as coordenadas 3D no mundo destes pontos considerando o modelo pinhole para a câmara. No caso da posição da mão é selecionado um ponto de entre os 21 para a definir ao longo do tempo, no entanto, para o cálculo da orientação foi desenvolvido um método auxiliar para estimação da pose tridimensional da mão denominado por “Iterative Pose Estimation Method” (ITP). Este método recorre aos dados 2D do Openpose e às coordenadas 3D do pulso de cada mão para efetuar a correta estimação das coordenadas 3D dos restantes pontos da mão. Isto permite essencialmente resolver problemas com oclusões da mão, muito frequentes com o uso de uma só câmara na gravação dos vídeos. Uma vez estimada corretamente a posição 3D no mundo dos vários pontos da mão, a sua orientação pode ser definida com recurso a quaisquer três pontos que definam um plano