1,721,022 research outputs found
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
Single-DC-Input Multi-Level Envelope Tracking of a High-Efficiency X-band Power Amplifier
No full textThis paper addresses the efficiency enhancement of microwave power amplifiers (PAs) with discrete-level supply-modulation. We demonstrate an efficient modulator architecture that generates three levels of drain supply voltages from a single dc voltage. Each level is stored in a "flying" capacitor that acts as a temporary voltage supply and is dynamically regulated by feedback through reversal of the PA drain current. A hybrid modulator based on GaN-on-Si technology is tested with a single-stage 2-W X-band MMIC PA with a drain efficiency of 55% at the peak output power. The overall average drain efficiency (PA and modulator) of up to 43% is measured with Gaussian-like pulses for radar and a 5-MHz 6-dB PAPR OFDM signal, and is improved up to 14 percentage points over a constant supply case, with normalized root mean square error below 1.5% when pre-distortion is used
Linearization of a 500-W L-band GaN Doherty Power Amplifier by Dual-Pulse Trap Characterization
No full textThis paper describes the linearization of a base-station L-band 500-W GaN Doherty high power amplifier (HPA) driven by OFDM signals. Pre-pulsing characterization is used to extract the gain dispersion of the carrier and peaking PAs due to trap-induced degradation of GaN-on-SiC transistors. Peak drain voltages reached by PA load-lines mainly set the trap states of the carrier and peaking PAs, while the recovery is longer with a dominant time constant of 100μs for this specific GaN technology. When the peak occurrences are below this dominant time constant of 100μs, such as for symbol periods of 16.7 to 66.7μs (i.e., LTE/5G OFDM), the HPA trap-state remains approximately constant in the time interval between voltage peaks, allowing low-complexity linearization of the HPA. With a 10-MHz OFDM signal with peak-to-peak intervals shorter than 100μs, a memory-less digital pre-distortion (DPD) is shown to improve ACLR by 4dB and NRMSE by 1.6 percentage points, as compared to peak-to-peak intervals longer than 100μs when significant trap recovery takes plac
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
Comparative analysis of heart- and pulse-rate variability during mental task execution: the role of pulse transit time variability
No full textHeart rate variability (HRV) analysis is an established method which provides valuable information on the autonomic nervous system’s (ANS) regulation of the cardiac rhythm. HRV is a time- and frequency-domain analysis which is based on the inter-beat interval series of normal sinus rhythm beats. Short-term HRV is computed over time frames of 5 minutes or less. It is widely used in biofeedback applications, in workload assessment and stress management.
In recent years different approaches have been proposed, in which the arterial blood pulse generated by cardiac contraction is used instead of the heart beat itself for generating the pulse-series. Although this approach simplifies signal acquisition as it only requires a photo-plethysmographic sensor (PPG) clipped to the earlobe or to a fingertip, the time occurring between heart contraction and propagation of the arterial blood pulse to the peripheral site may determine non-negligible differences between electrocardiogram-derived HRV and PPG-derived HRV indices.
Aim of this study is to present a comparative analysis of short-term indices of electrocardiogram-derived HRV and PPG-derived HRV, in an experimental setup reproducing the scenario of a sedentary working activity
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
Effects of working memory demand on short-term heart-rate- and pulse transit time-variability
No full textThe Sternberg memory scanning task provides a measure of processing and working memory retrieval speed. In this test, subjects are presented a set of stimuli of given length. After a delay, one item is presented, and subjects are asked to indicate whether or not the item was part of the set. Performance is assessed by speed and accuracy of the response.
Short-term heart rate variability (HRV) analysis is an eligible method for assessing the autonomic nervous system (ANS) mediated response of the cardiovascular system to working memory allocation and retrieval effort.
Pulse transit time (PTT), namely the interval between heart systole and arterial blood pulse (PPG) detected in peripheral sites, has also been related to mental stress.
The purpose of this study is to analyse HRV and PTT variability (PTTV) in response to a stepwise-increasing difficulty Sternberg task
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