1,721,044 research outputs found
A comparative test of different compression methods applied to solar images
No full textIn this work we conduct a comparative study on different data compression methods applied to high resolution images of the solar surface acquired at the Solar Dunn Telescope in Sacramento Peak with the IBIS (Interferometric Bidimensional Spectrometer) instrument. Our aim is to perform an estimation of the quality, efficiency and workload of the considered computing techniques both in the so-called lossless modality, where in the reconstruction phase there is no loss of information, and in lossy mode, where it should be possible to reach a high compression ratio at the expense of image information. In the latter case we quantify the quality with image analysis conventional methods and more specifically with the reconstruction of physical parameters through standard procedures used in this kind of observations. The considered methods constitute the most frequently adopted image compression procedures in a variety of fields of application; they exploit in different ways the properties of the Discrete Wavelet Transforms often coupled with standard entropy coders or similar coding procedures applied to the different bit planes in order to allow a progressive handling of the original image. In the lossless approach we found that all methods give a compression ratio around 2. For a lossy compression we reached a compression ratio of 8 (equivalent to a 2 bit per pixel) without any perceptual difference between original and reconstructed images, but with effects on the photometric accuracy. We also tested the performance of 3-D lossy methods for the compression of data-cubes. Maintaining the same data degradation level, those methods allows us to gain a 2x in the compression ratio over the 2-D methods
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
Three-minute wave enhancement in the solar photosphere
Full text linkIt is a well-known result that the power of five-minute oscillations is progressively reduced by magnetic fields in the solar photosphere. Many authors have pointed out that this could be due to a complex interaction of many processes: opacity effects, MHD mode conversion, and intrinsically weaker acoustic emissivity in strong magnetic fields. While five-minute oscillations predominate in the photosphere, it has been shown that in the chromosphere three-minute oscillations are more common. Two main theories have been proposed to explain the presence of the latter oscillations based upon resonance filtering in the atmospheric cavity and non-linear interactions. In this work, we show, through the analysis of IBIS observations of a solar pore in the photospheric Fe I 617.3 nm line, that three-minute waves are already present at the height of formation of this line, their amplitude depends on the magnetic field strength, and they are strictly confined to the umbral region
L'Etnomusicologia e le musiche contemporanne, Seminario Internazionale di Studi 2007.
No full textGli studi antropologico-musicali hanno definito e studiato ampiamente le funzioni della musica nelle società agricolo-pastorali. Dopo una discussione sul significato in antropologia del termine funzione, l'articolo presenta una serie di situazioni per analizzare l'uso e il valore della musica in realtà contemporanee: un rituale di un culto di possessione ugandese in cui viene usata anche musica commerciale, i balli di gruppo in sale da ballo italiane, la correlazione musica-movimento nelle palestre
Magnetic energy balance in the quiet sun on supergranular spatial and temporal scales
Full text linkSmall-scale magnetic fields are ubiquitous in the quiet solar photosphere and may store and transfer huge amounts of energy to the upper atmospheric layers. For this reason, it is fundamental to constrain the energetics of the quiet Sun. By taking advantage of a 24 hr long magnetogram time series acquired by the Hinode mission without interruption, we computed, for the first time, the average rate of change of magnetic energy density on supergranular spatial and temporal scales. We found that the regions where this quantity is positive correspond with the longest magnetic field decorrelation times, with the latter being consistent with the timescales of magnetic energy density variation. This suggests that, on average, the energy provided by photospheric electric and magnetic fields and current density is effective in sustaining the magnetic fields in the network
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
Sessanta anni di etnomusicologia in Italia: nuove sfide disciplinari e istituzionali (in collaborazione con Francesco Giannattasio)
No full textThe paper presents a critical review of the history of Ethnomusicology in Italy between 1948 and 2008
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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