1,720,959 research outputs found
Precise doppler measurements for navigation and planetary geodesy using low gain antennas: test result from Cassini
No full textESA ∆DOR enhancement: agencies interoperability, wideband and low-SNR functionality
No full textDelta Differential One-way Ranging (ADOR) is a powerful method used for navigation of interplanetary probes. It provides a direct measurement of the angular position of a spacecraft using interferometric techniques to obtain the difference in the arrival time of a spacecraft signal received at two ground stations, using an ICRF (International Celestial Reference Frame) quasar as a reference. In 2005, Sapienza University of Rome undertook the development of a ADOR correlator for the European Space Agency, expanding the tools available for the operation of European planetary and astrometric missions. Since its delivery, the correlator has been successfully used for the orbit determination of Venus Express and Rosetta. In a later release the correlator's capabilities were expanded to accept data acquired not only at ESA's ESTRACK stations, but also at VLBI and NASA's Deep Space Network antennae. In 2011 ESA and Sapienza University have undertaken further enhancements of the correlator, by expanding the accepted data formats, extending the total spanned bandwidth and enabling the correlation of very-low SNR signals. The new Raw Data Exchange Format, RDEF, established by the Consultative-Committee for Space Data Systems (CCSDS) in order to increase the ADOR interoperability between different agencies has been implemented in the correlator. This enhancement will allow the direct processing of data acquired by different agencies. The second additional functionality provided an improved determination of the quasar and spacecraft delay by increasing the spanned bandwidth of the recorded signal. Due to current hardware limitations, the bandwidth at ESTRACK stations is currently limited to 28 MHz. ESA is planning to use three LDC (L-band Down-Converter) to acquire different portion of the signal spectrum, and route the signal to up to three IFMS receivers (Intermediate Frequency Modulation System). With this configuration the total spanned bandwidth could be increased up to 220 MHz at Ka-band. The enhanced version of the correlator is capable of handling this new configuration and take advantage of the wider bandwidth. Finally, a third enhancement enabled the correlation of narrowband, low-SNR, spacecraft signals. Although the correlator can operate in several modes, the processing of the spacecraft signal is currently carried out by means of a master phase locked loop (PLL) on the carrier and slave PLLs on the telemetry harmonics. A new PLL-free algorithm for the spacecraft data correlation allows the processing of low-SNR signals (up to 1 dBHz). Such weak signals cannot be tracked by a standard PLL (hardware or software)
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
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
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
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