1,721,008 research outputs found
Development of a new global rainfall rate model based on ERA40, TRMM, GPCC and GPCP products
No full textThis paper presents the study carried out to improve the accuracy of the rainfall rate prediction model in Rec. ITU-R P.837-4. By combining different precipitation data sources, new global maps of the model input parameters have been calculated, which guarantee both higher accuracy and spatial resolution. An optimization of model coefficients has been performed by considering cumulative distribution functions (CDFs) of measured rainfall rate, provided by DBSG3, which were selected by taking into account their quality, worldwide distribution and statistical stability in terms of years of measurements. The results show that the prediction of the mean annual rainfall rate distribution is improved of ~10% and ~25% in terms of bias and root mean square of the relative estimation error, respectively. An attempt in estimating intra-annual rain rate has also been carried out, showing promising results that call for a larger collection of measured monthly rainfall rate CDFs
Characterization and modelling of time diversity statistics for satellite communications from 12 to 50 GHz
No full textTo compensate propagation impairments on Earth–space communication links, a specific fade mitigation technique to make up for rain propagation impairments is studied in this paper: the time diversity. This process consists in sending the information when the propagation channel allows to get it through. Here the time diversity technique is applied to different experimental attenuation time series collected in Europe: Spino d’Adda (Italy), Louvain-la-Neuve and Lessive (Belgium). These propagation measurements have been collected from 12 to 50 GHz and the performance of time diversity technique is assessed from the generation of time diversity statistics conditioned to the time delay. A prediction method of these statistics is also described. The proposed model relies on the time correlation of the attenuation time series. The model is validated and its accuracy analysed in terms of prediction error calculated using the different databases
Performance of the synthetic storm technique in a low elevation 5° slant path at 44.5 GHz in the French Pyrénées
No full textWe show that the Synthetic Storm Technique can be
applied to slant paths of very low elevation angle, but
with caution and some limitations. To this end, we have
processed the rain attenuation measurements collected
in the years 1999 and 2000, in a 5° slant path radio link
at 44.5 GHz between the top of Pic du Midi (altitude
2865 m) and Lannemezan (altitude 600 m), a 28-km
path length, in the French Pyrénées (experiment known
as CELESTE), to obtain the exceedance probability
distributions of rain attenuation and fade duration. Then
we have compared the experimental distributions to
those predicted by the Synthetic Storm Technique with
strictly concurrent measurements of rain rate time
series. We have found that if the rainy path length
assumed in the Synthetic Storm Technique modeling is
limited to 13~15 km, instead of 28 km, then, for a large
attenuation range: (a) the probability distribution of rain
attenuation is well reproduced; (b) the experimental
probability distribution of fade duration is well
reproduced for fade durations longer than about 10
minutes
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
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