1,721,011 research outputs found
Ionospheric Doppler measurements by means of HF-radar techniques
No full textStudies of the dynamics of the ionosphere and its related phenomena are mainly based on Doppler Drift measurements.
The time variation (ionisation/recombination) of plasma density, thermospheric wind and others can
be observed by means of HF-radars. The technique of Doppler Drift measurements is a quite complex technique
that is now affordable by means of an advanced ionospheric sounder. The combination of vertical sounding and
interferometric Doppler detection discloses the Doppler sources. The echo signal contains the Doppler shift in
frequency imposed on the wave carrier by each point source where the signal is reflected. Other phenomena like
environmental noise and the intrinsic error of the measurements that, together with the change in time of the refractive
index, affect the measurements in various ways impeding to better quantify the results.JCR Journalope
Quasi-five- and ten-day oscillations in f0F2 and their possible connection with oscillations at lower ionospheric heights
No full textThe statistical analysis of the 5-day and 10-day oscillations inferred in the upper and lower ionosphere in Central Europe from f0F2 measured in Pruhonice and the radio wave absorption in the lower ionosphere shows a remarkable degree of similarity for relative amplitudes of oscillations (not for absolute amplitudes). The relative amplitudes in both regions do not express a significant solar cycle effect and their seasonal variation is also similar except for winter. The typical relative amplitude of both 5- and 10-day oscillations in the F2-region is about 4%, which is useful information for PRIME.JCR Journalope
From COST 271 to 296 EU actions on ionospheric monitoring and modelling for terrestrial and Earth-space radio systems
No full textThe ionospheric community has long been aware that co-operative research on an international basis is essential to deal with temporal
and spatial changes in the ionosphere that influence the performance of terrestrial and Earth-space radio systems. The EU COST (Cooperation
in the field of Scientific and Technical Research) 271 Action on "Effects of the Upper Atmosphere on Terrestrial and Earthspace
Communications" has had during the period of October 2000-August 2004 the following main objectives: (1) to evaluate the influence
of upper atmospheric conditions on terrestrial and Earth-space communications, (2) to develop methods and techniques to improve
ionospheric models over Europe for telecommunication and navigation applications and (3) to transfer the results to the appropriate
radiocommunication study groups of the International Telecommunication Union (ITU-R) and other national and international
organizations dealing with the modern communication systems.
At the beginning of 2005 the new 296 Action in the COST Telecommunications, Information Science and Technology domain on
"Mitigation of lonospheric Effects on Radio Systems (MIERS)" was approved for the period 2005-2009. The main objectives of the
MIERS are: (a) to support and enhance the existing European facilities for historical and real-time digital ionospheric data collection
and exchange; (b) to develop an integrated approach to ionospheric modelling, create the mechanism needed to ingest processed data
into models, extend and develop suitable mitigation models and define the protocols needed to link models together; and (c) to strengthen
the areas of expertise that already exist by stimulating closer cooperation between scientists and users, focusing the scope of all the previous
COST ionospheric related studies to the mitigation of ionospheric effects on radio systems.
This paper summarises briefly how the major objectives of the COST27l Action have been achieved and what are the most important
activities to be undertaken in the follow-on COST296 Action.Published899-9033.9. Fisica della magnetosfera, ionosfera e meteorologia spazialeN/A or not JCRreserve
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
Predicted and measured bottomside F-region electron density and variability of the D 1 parameter under quiet and disturbed conditions over Europe
Full text linkModelling and forecasting of ionospheric parameters is very useful for different radio communication purposes. As long as variations in the ionosphere form regular patterns, the empirical International Reference Ionosphere model, IRI 2000, provides sufficiently accurate corrections to the maximum electron density, N m F2, to predict the ionospheric effects on radio wave propagation. During geomagnetic storms, however, agreement between the IRI 2000 model and observations is still insufficient. This paper deals with the analysis of measured and model predicted F-region electron densities under quiet and disturbed conditions with the main emphasis placed on the distribution of the F1-region daytime ionisation. Available electron density profiles obtained from ionograms for selected periods from several European ionospheric stations (Pruhonice, Ebro, Arenosillo) were compared with IRI 2000 model results. Comparative analysis shows that discrepancies do exist predominantly during the storm main phase. The model predicted daytime electron densities at the fixed Fl-region heights are closer to observed values during summer than winter. Dependences of D 1 on solar activity and season are also analysed.Fil: Buresova, D.. Academy of Sciences of the Czech Republic; República ChecaFil: Altadill, D.. Observatory d’Ebro; EspañaFil: Mosert, Marta Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Miro, G.. Abdus Salam International Centre for Theoretical Physics; Itali
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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