1,720,973 research outputs found
A single-station model suitable for f0F2 mapping
No full textIonospheric monthly-median values of the F2 and E layer critical frequencies from 24 mid-latitude European stations are fitted to a second degree polynomial and their correlation is discussed. The resulting model is used to predict monthly-median f0F2 values for different ionospheric stations and for high, medium and low ionospheric activity. Finally, a potential application of the single station model developed for Slough to mapping the F2-layer critical frequency is investigated. Thus prediction of the monthly median f0F2 values for eight mid-latitude European stations is attempted using the single-station model of Slough and the corresponding F0E values of the station under investigation. The f0F2 values obtained are reasonably accurate. The main advantage of this method is its simplicity and the restricted number of parameters used.JCR Journalope
The effects of f0 F2 variability on TEC prediction accuracy
No full textIn this paper hourly daily F2-layer critical frequency data recorded at Rome and one minute daily TEC data recorded at Florence were used and the relevant variabiles were calculated. It was concluded that there was no clear evidence as to how they correlated. In order to obtain a measure of the f 0 F 2 and TEC variability, the normalised differences df0 F2 and d TEC from the relevant monthly median values were also considered. Since no clear evidence could be obtained as of how df0 F2 and d TEC correlate, a new parameter, the ?Ap /?R ratio was tried. ?Ap was taken as the difference between the maximum value of Ap measured at the relevant disturbance and that corresponding at the beginning of the disturbance. ?R corresponded to the two above mentioned values of Ap. This parameter was compared to the differences of the corresponding df0 F2 values called ?df and d TEC values called ?dT. In wintertime, when ?A p /? R was negative, for the vast majority of the occurrences either ?df or ?dT was negative; ?df and ?dT were never observed to be negative at the same time whereas they were both positive in fewer than 10% of the observations. When ?A p /?R was positive then either ?df or ?dT were negative. In summertime when ?A p /?R was negative both ?df and ?dT were negative. When ?A p /?R was positive, while a positive ?df corresponded almost always to a positive ?dT, a negative ?df would equiprobably indicate either a positive or a negative ?dT.PublishedJCR Journalope
Ten years analysis of Tropospheric refractivity variations
No full textThe refractivity variations of the troposphere are responsible for various effects on radio wave propagation, such as refraction, bending, radio-station interference, etc. In this work, the refractivity variations of the Hellenic
troposphere are studied using data from Helliniko airport of Athens/Greece. The data were analyzed using various interpolation procedures, i.e. in a day-by-day manner for temperature and relative humidity, to transform the data according to a reference height common for the whole dataset and finally for the refractivity
N with respect to time, using piece-wise hermite interpolation polynomials for the low and medium altitudes and linear interpolation factors for the high altitudes. Since refractivity varies with time and height, two height independent basic parameters were computed and analyzed: the refractivity at station height N0 and scale height Hs. These parameters can be used to calculate the refractivity profile. Using statistical tools as the moving average, the ß0 parameter and the monthly mean values, together with the corresponding standard deviations, useful results were obtained for the variations of the refractivity with respect to observation hour, height, season, month, day and level.PublishedJCR Journalope
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Correlations in daily deviations from the median of f0F2, M(3000)F2 and VF
No full textThe statistical analysis of the hourly daily deviations from the corresponding monthly-median values of the factor M(3000)F2 and of the critical frequency of the F2-layer, f0F2, reveals that the correlation between these parameters is poor. A similar analysis between the hourly daily deviations from the corresponding monthly-median of the height h’F and the f0F2 leads to similar results. These results indicate that the factor M(3000)F2, the height h’F and the critical frequency f0F2 may have a different daily variability.JCR Journalope
Assessment of the solar-cycle dependence of f0F2 1157
No full textComparisons between observed hourly monthly-median values of f0F2 at Slough and Rome, and calculated f0F2 values using as an index of solar activity R12 or T12, demonstrate that there is practically no difference in the results when a solar (e.g., R12) or ionospheric index (e.g., T12) is used. The choice of the index should be based on other criteria. It is also shown that there is a slight degree of favourability for a quadratic law between f0F2 and each index of solar activity. Therefore, in mapping F-layer characteristics a second-degree relation should be adopted independently of rising or falling solar-cycle. Saturation and hysteresis effects could be then minimised.JCR Journalope
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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