1,720,956 research outputs found
Analysis and design of a 195.6 dBc/Hz peak FoM P-N class-B oscillator with transformer-based tail filtering
Full text linkA complementary p-n class-B oscillator with two magnetically coupled second harmonic tail resonators is presented and compared to an N-only reference one. An in depth analysis of phase noise, based on direct derivation of the Impulse Sensitivity Function (ISF), provides design insights on the optimization of the tail resonators. In principle the complementary p-n oscillator has the same optimum Figure of Merit (FoM) of the N-only at half the voltage swing. At a supply voltage of 1.5 V, the maximum allowed oscillation amplitude of the N-only is constrained, by reliability considerations, to be smaller than the value that corresponds to the optimum FoM even when 1.8 V thick oxide transistors are used. For an oscillation amplitude that ensures reliable operation and the same tank, the p-n oscillator achieves a FoM 2 to 3 dB better than the N, only depending on the safety margin taken in the design. After frequency division by 2, the p-n oscillator has a measured phase noise that ranges from -150.8 to -151.5 dBc/Hz at 10 MHz offset from the carrier when the frequency of oscillation is varied from 7.35 to 8.4 GHz. With a power consumption of 6.3 mW, a peak FoM of 195.6 dBc/Hz is achieved.This work was supported by the European Marie Curie IAPP Grant Agreement N 251399.info:eu-repo/semantics/publishedVersio
A 195.6dBc/Hz peak FoM P-N class-B oscillator with transformer-based tail filtering
Full text linkA complementary p-n class-B oscillator with two magnetically coupled second harmonic tail resonators is presented. For the same oscillation amplitude (constrained by reliability considerations) and the same tank, the p-n oscillator achieves 3-4dB better Figure of Merit (FoM) than an n-only reference one. After frequency division by 2, the p-n oscillator has a measured phase noise that ranges from -150.8 to -151.5 dBc/Hz at 10MHz offset from the carrier when the frequency of oscillation is varied from 3.64 to 4.15GHz. With a power consumption of 6.3mW, a peak FoM of 195.6 dBc/Hz is achieved.This work was supported by the European Marie Curie Grant Agreement No 251399. Paulo Mendes research was partially supported by grant SFRH/BSAB/1245/2012.info:eu-repo/semantics/publishedVersio
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
Monitoring morphological changes in a glacier environment based on multitemporal structure-from-motion photogrammetry
No full textLAUREA MAGISTRALEIl presente studio si propone di determinare se i modelli topografici di un'area soggetta a significative modifiche morfologiche, prodotti grazie al metodo SfM (Structure-from-Motion) da immagini acquisite con fotogrammetria aerea durante diverse epoche, possano essere confrontati senza la necessità di georeferenziazione basata su punti di riferimento terrestri acquisiti in ciascun periodo.
L'obiettivo principale consiste nell'esaminare la possibilità di utilizzare un'unica acquisizione di punti di appoggio a terra, effettuata con strumentazione GNSS in un dato periodo, per confrontare il modello digitale del terreno in diverse epoche.
L’evoluzione tecnologica del settore dei rilevamenti terrestri comporta che la strumentazione utilizzata per l’acquisizione delle informazioni per la ricostruzione di modelli fotogrammetrici sia in continuo miglioramento, con livelli di precisione, qualità e accuratezza sempre migliori.
Il metodo presentato in questa tesi per riuscire ad allineare diverse nuvole di punti, georeferenziarle correttamente nello spazio e ottenere la possibilità di valutare possibili cambiamenti morfologici del terreno, è stato condotto riferendosi al monitoraggio della lingua e della parte terminale del Ghiacciaio dei Forni (Alpi Retiche, Italia), situato nel Parco Nazionale dello Stelvio.
Proprio per la natura di questi luoghi, durante l’acquisizione delle immagini aeree nelle diverse epoche (dal 2014 al 2021), non sempre è stato possibile acquisire punti a terra con strumentazione GNSS per la georeferenziazione, oltre al fatto che la strumentazione utilizzata per l’acquisizione delle immagini stesse è cambiata nel tempo.
Da qui l’esigenza di trovare una metodologia che potesse rendere utilizzabile tutto il dataset a disposizione.
Utilizzando il software di fotogrammetria Agisoft Metashape, è stato possibile allineare tutte le immagini con un’unica elaborazione, georeferenziare la nuvola di punti di legame ottenuta, suddividerla in più nuvole, ciascuna secondo la propria epoca di riferimento, e generare le rispettive nuvole dense. Grazie all’utilizzo del software Cloud Compare, è stato possibile visualizzare e calcolare le modifiche morfologiche del terreno, escludendo variazioni significative al di fuori del corpo glaciale.
I risultati hanno dimostrato che, grazie ai punti di controllo a terra di una sola epoca, è stato possibile utilizzare tutto il dataset a disposizione ottenendo con un’ottima precisione i volumi di ghiaccio persi, lo spostamento e la velocità di assottigliamento del ghiacciaio su scale di tempo annuali.
La metodologia in esame può essere applicata in diversi ambiti per il monitoraggio delle modifiche morfologiche di una superficie, specialmente in contesti montani e in aree difficilmente accessibili.
Dopo il primo rilevamento, effettuato utilizzando punti di riferimento terrestri, i successivi monitoraggi possono essere condotti in modo efficiente da un singolo operatore UAV, senza la necessità di acquisire nuovamente i dati di georeferenziazione.
Questo approccio comporta risparmi significativi in termini di tempo, risorse umane e complessità computazionale durante la fase di elaborazione. L’unico prerequisito fondamentale è la presenza di blocchi stabili all'interno del dominio soggetto al rilevamento aerofotogrammetrico, riconoscibili come tali dal software SfM, come ad esempio opere di ingegneria idraulica o strutture artificiali.
Infine, una dimostrazione dell’applicazione del metodo per il monitoraggio del trasporto solido in un torrente montano è presentata nel penultimo capitolo del presente elaborato.The aim of this study is to determine whether topographic models of an area undergoing significant morphological changes, generated using the SfM (Structure-from-Motion) method from aerial photogrammetry images acquired in different epochs, can be compared without the need for georeferencing based on ground reference points acquired in each epoch.
The main objective is to investigate the possibility of using a single acquisition of ground reference points made with GNSS instruments during a given period to compare the digital terrain model during different epochs.
The technological evolution of the land surveying sector means that the instrumentation used to acquire information for the reconstruction of photogrammetric models is constantly improving, with ever higher levels of precision, quality, and accuracy.
The method presented in this work, which allows the alignment of different point clouds, their correct spatial georeferencing and the possibility of assessing possible morphological changes in the terrain, has been applied to the monitoring of the tongue and terminal part of the Forni Glacier (Rhaetian Alps, Italy), located in the Stelvio National Park.
Due to the nature of these sites, during the acquisition of aerial images at different times (from 2014 to 2021), it was not always possible to acquire points on the ground with GNSS instrumentation for georeferencing, in addition to the fact that the instrumentation used to acquire the images themselves has changed over time.
It was therefore necessary to find a method that could make use of the entire available data set.
Using Agisoft Metashape photogrammetry software, it was possible to align all the images in a single operation, georeferenced the resulting cloud of tie points, subdivide it into several clouds, each according to its own reference epoch, and generate the corresponding dense clouds. Using the Cloud Compare software, it was possible to visualise and calculate the morphological changes in the terrain, excluding significant variations outside the glacier body.
The results showed that, thanks to the ground control points of a single epoch, it was possible to use the entire available dataset and obtain the volume of ice lost, the displacement and the thinning rate of the glacier on annual time scales with excellent accuracy.
This method can be applied in various fields to monitor the morphological changes of a surface, especially in mountainous contexts and in areas that are difficult to access.
After the initial survey using terrestrial reference points, subsequent monitoring can be efficiently carried out by a single UAV operator without the need to re-acquire georeferencing data.
This approach results in significant savings in terms of time, human resources and computational complexity during the processing phase. The only basic requirement is the presence of stable blocks within the area to be aero photogrammetrically surveyed, recognisable as such by the SfM software, such as hydraulic works or man-made structures.
Finally, a demonstration of the application of the method to the monitoring of sediment transport in a mountain stream is presented in the penultimate chapter of this work
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
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