1,720,983 research outputs found
Application of the embedded model control to satellite-to-satellite tracking for future Earth observing missions
No full textSatellite-to-satellite tracking for future Earth observation missions: the Embedded Model Control approach
No full textEmbedded Model Control application to drag-free and satellite-to satellite tracking
No full textThis paper describes the realization of a generic simulator for formation flying satellites, and the design and application of Embedded Model Control (EMC) to the spacecraft control, as potentially applicable to a constellation of drag-free satellites. They can be employed for scientific purposes: here it is presented the Satellite-Satellite Interferometry (SSI) mission for the measurement of the Earth's gravitational field harmonics, which will follow the incoming gravimetric mission GOCE and the gravitational wave observatory LISA. The core drag-free controller (DFC) was partly validated by Preliminary Design Review of GOCE mission, and particular emphasize is given to the acceleration observer and to the command computation law. The measurement model and mission requirements are also presented, followed by the simulation results of the DFC, tuned ad-hoc in order to obtain accurate aiming targe
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
Laser metrology concept consolidation for NGGM
No full textThe measurement of the static and temporal variation of Earth’s gravity field yields important information on water storage, seasonal and sub-seasonal water cycles, their impact on water levels and delivers key data to Earth’s climate models. The satellite missions GOCE (ESA), GRACE (US-GER) and just recently GRACE Follow-On (US-GER) resulted in a significant improvement on our understanding of the system Earth. To further improve the measurement accuracy of the time-variable gravity field, ESA is investigating the concept of a ‘Next Generation Gravity Mission’ (NGGM), consisting of two pairs of satellites and a heterodyne laser interferometer for inter-satellite ranging. Based on the heritage of the development of the laser ranging interferometer for GRACE Follow-On and the former and ongoing studies for NGGM, two schemes for the Laser Metrology Instrument (LMI) for NGGM, namely the transponder and the retroreflector scheme have been investigated and are presented in this paper. The results include the instrument ranging performance analyses, the laser link acquisition, an instrument reliability assessment and redundancy approach as well as the Technology Readiness Level assessment of the individual instrument units
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