1,720,986 research outputs found
A Soft-Defined Pulse Width Modulation Approach-Part II: System Modeling
No full textIn this work we model from a system design perspective the realization of a novel mixed-signal approach to pulse width modulation (PWM). The working principle for the approach, along with an implementation scheme comprised of a digital zero-positioning (ZP) followed by a proper digital-to-analog converter (DAC) and comparator, has been introduced in a companion paper. We here focus on analyzing the global system in order to get a model of its performances in terms of dynamic range and non-linearity. Since non-linearities and quantization noise occur between the ZP and the comparator, firstly, upstream models for them are provided; then their effect on the PWM signal is calculated by means of a downstream model of perturbations at the input of an ideal natural sampling PWM. Finally, an exhaustive formula for the resulting dynamic range is given and some configurations of practical interest are proposed
A Soft-Defined Pulse Width Modulation Approach - Part I: Principles
No full textIn this work a novel pulse width modulation (PWM) scheme is presented consisting of a mixed digital-analog implementation. The aim of this approach is to obtain maximum flexibility in setting and varying the average switching frequency, as a method to optimally deal with specifications concerning power consumption and bandwidth management. Conventional analog implementations of PWM suffer from inaccuracy due to circuit-level parameters deviation and bandwidth limitations, whereas digital implementations are subject to restrictions imposed by time quantization. Conversely, our mixed approach accurately reproduces the theoretical, natural sampling PWM output without directly comparing the modulating signal to a piecewise-linear carrier, either in the analog or the digital domain. Instead, the proposed design compares suitably pre-distorted versions of both the carrier and the modulating signals, so that their crossing points are not altered. The resulting bandwidths are relatively small to allow a non-aliased discrete-time synthesis. After digital-to-analog conversion, the PWM signal is finally obtained by a simple comparator. We support the proposed design by measuring the PWM spectrum as synthesized by a proof-of-concept prototype
Excitations and signal processing for multiprobe setups
No full textThe possibility of taking advantage of multiprobe setups for ultrasound non-destructive testing (NDT) is introduced with reference to its physical and signal processing aspects. Preliminarily, a major distinction is made between phased-arrays and actual multi-transducer configurations. Then, most of the chapter is devoted to the latter type of setup. In this framework, the previously introduced channel model developed for single-probe operation, is extended to setups featuring multiple transmitting transducers (TXs) and receiving transducers (RXs) meant to be employed simultaneously in a so-called multiple input, multiple output (MIMO) configuration. It is also illustrated how this configuration relates to multi-user communication networks. Proper merit factors suitable for characterizing the performances of multiprobe systems are presented by taking advantage of the probabilistic system view introduced for single-probe systems. Finally, various classes of signals that can be adopted in MIMO NDT systems are described. These excitations may be designed according to random or deterministic approaches. In better detail, special techniques based on tessellation of the time-frequency (TF) plane are developed to design excitation signals capable of joining assuring contextually the good degree of appropriateness for MIMO setups and the good signal-to-noise (SNR) and resolution properties of chirps
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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