1,721,160 research outputs found
The long-term stability of the visible F corona at heights of 3–6
No full textContext.CMEs can effect the distribution of dust grains in the corona. The brightness of the visible F corona is expected therefore to change as the frequency of CMEs varies with solar cycle.
Aims.We search for a variation in the F corona by comparing LASCO C2 observations from solar minimum and maximum.
Methods.An established inversion method is used to calculate the visible F corona brightness from LASCO C2 solar minimum observations made during 1996/10. Good agreement is found with the F corona brightness calculated from Skylab observations during 1973/05–1974/02 for heights of 3–6 . The unpolarized brightness, which is dominated by the unpolarized F corona brightness at these heights, is obtained by subtracting many pairs of polarized brightness images from total brightness images and averaging over a solar rotation. We calculate the unpolarized brightness for both solar activity minimum and maximum.
Results.The unpolarized brightness, and therefore the F corona, remain virtually unchanged between solar minimum and maximum at heights above 2.6 , despite the large change in the shape and activity of the corona. Using a simple density model, it is shown that the small variation in unpolarized brightness seen below 2.6 can arise from differences in the distribution of electron density, and therefore cannot be attributed to a variation in the F corona.
Conclusions.Despite the large rise in frequency of CMEs from solar minimum to maximum, the F coronal brightness, at heights of 3–6 in the visible, remains very stable
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
Dermatomiosite giovanile : malattia rara ed estremamente polimorfa : Possibili indicatori prognostici precoci
No full textVariations 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
Measuring the F-corona intensity through time correlation of total and polarized visible light images
Full text linkWe present a new correlation method for deriving the F-corona intensity distribution, which is based on the analysis of the evolution of the total and polarized visible light (VL) images. We studied the one-month variation profiles of the total and polarized brightness acquired with Large Angle Spectrometric COronagraph and found that in some regions they are highly correlated. Assuming that the F-corona does not vary significantly on a timescale of one month, we estimated its intensity in the high-correlation regions and reconstructed the corresponding intensity maps both during the solar-minimum and solar-maximum periods. Systematic uncertainties were estimated by performing dedicated simulations. We compared the resulting F-corona images with those determined using the inversion technique and found that the correlation method provides a smoother intensity distribution. We also obtained that the F-corona images calculated for consecutive months show no significant variation. Finally, we note that this method can be applied to the future high-cadence VL observations carried out with the Metis/Solar Orbiter coronagraph
Observations of the Solar F-corona from Space
No full textThe observations of the solar F-corona from space are reviewed emphasizing
the 25 years of continuous monitoring achieved by the LASCO-C2 and C3
coronagraphs. Our work includes images obtained by the Clementine cameras, and
the STEREO/SECCHI/HI-1A and PSP/WISPR heliospheric imagers. The characteristic
radiance profiles along the equatorial and polar directions follow power laws
in the 5{\deg}-50{\deg} range of elongation, with constant power exponents of
-2.33 and -2.55. Both profiles connect extremely well to the corresponding
standard profiles of the zodiacal light. The LASCO equatorial profile exhibits
a shoulder implying a 17% decrease of the radiance within 10Rsun that may be
explained by the disappearance of organic materials within 0.3 AU. LASCO
detected for the first time a secular variation of the F-corona, an increase at
a rate of 0.46% per year of the integrated radiance in the LASCO-C3 FoV. This
is likely the first observational evidence of the role of collisions in the
inner zodiacal cloud. A composite of C2 and C3 images produced the LASCO
reference map of the radiance of the F-corona from 2 to 30Rsun and, by
combining with ground-based measurements, the LASCO extended map from 1 to 6
Rsun. The plane of symmetry of the inner zodiacal cloud is strongly warped, its
inclination increasing towards the planes of the inner planets and ultimately
the solar equator. In contrast, its longitude of ascending node is found to be
constant and equal to 87.6{\deg}. LASCO did not detect any small-scale
structures such as putative rings occasionally reported during solar eclipses.
The outer border of the depletion zone where interplanetary dust particles
start to be affected by sublimation appears well constrained at 19Rsun. This
zone extends down to 5Rsun, thus defining the boundary of the dust-free zone
where the most refractory materials, likely moderately absorbing silicates,
disappear.Comment: 85 pages, 42 figures, 5 table
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
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