1,721,492 research outputs found
Tropospheric scintillation and attenuation on satellite-to-Earth links at Ka and Q band: modeling, validation and experimental applications
Full text linkLink budget is a crucial step during the design of every communication system. For
this reason it is fundamental to identify and estimate the effects of the atmosphere
on the electromagnetic signal along the path from the source to the sink. Troposphere
represent the bigger source of attenuation and scintillation for signals in the
microwave and upper frequency spectrum. During last years we have participated
in the European Space Agency “AlphaSat Aldo Paraboni” experimental campaigns
to acquire up to date propagation data at two frequencies of interest for future
communication systems. We realized two high performance low-noise receiver located
in Rome, one at Ka and one at Q band (19.701 and 39.402 GHz) to detect the two
signal beacons sent from the AlphaSat geostationary satellite to a wide area over
Europe. Collected data from Rome receiving station have been analysed to measure
excess attenuation and scintillation along the path. Such statistics collected in a
database together with data from other experimenter will be in the near future a
useful instrument, giving professionals updated data for their custom application
design.
Classical link budget techniques rely on climatological atmospheric statistics
based on different time-scales, usually data collected for several years. In the
background of the European Space Agency “STEAM” project, we proposed the use
of high resolution 3D weather forecast models (up to 166m pixel resolution) for the
calculation of excess attenuation and tropospheric scintillation for satellite to earth
link. As a result, the estimation of these electromagnetic parameters to use in link
budgets could be given no more as a statistical analysis of past events as in the
case of Internation Telecommunication Union recommendation but as time-series
forecast specific for the selected receiving station and along the slant path of the
transmitted signal. Case studies for the use of this technique have been deeply
analysed and results compared with data from the AlphaSat measurement campaign
for the Rome and Spino d’Adda receiving station, confirming the validity even in
different geographical regions.
In everyday situations, propagation models based on statistics are often replaced
by the use of easier to apply parametric models. Those have the advantage of
the simplicity and the need of less input parameter to be applied. In particular,
for what concerning the tropospheric scintillation, the Hufnagel-Valley refractive
index structure constant (C2n
) parametric model is actually the most used, due to
the simplicity and the relative accuracy. We here propose a new Cn2 polynomial
parametric model (CPP) based just on the altitude z and a function C2 n0(to,RH0)
that allow to calculate the ground refractive index structure constant just using the
ground temperature (T0) and the relative humidity (RH0). In this work CPP and
Hufnagel-Valley models are applied to different location around the globe to prove
their accuracy. The obtained model could be also used in the future to realize a
simulator able to generate random C2n
vertical profiles specific for the receiver site
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
A Theoretical description of the trans- cis conversion in the lowest excited states of diimide. A comparison of different methods for the calculation of excited state wave functions
No full textThe lowest excited states of the diimide molecule have been calculated by
three different SCF-type methods, the performances of which are analyzed in
regard to the prediction of geometries and energies.
The calculations have been performed with two basis sets (STO-3G and 4-31G) both supplemented with more diffuse functions on the N atoms.
Lowest energy pathways for the trans-cis interconversion in the various states are presented for the three calculation methods and for the two basis sets
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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