1,720,998 research outputs found
Optimising Landing-site Selection for ExoMars
No full textOnly 6 out of 16 missions to the surface of Mars have been successful, all have been NASA missions. The landing sites of all the successful missions have been carefully selected in a process where: 1) scientists propose candidate landing sites, 2) engineers check whether these sites allow for a safe landing, and 3) over a few iterations, the number of sites is brought down to the final site and a back-up. ExoMars will be the first lander to Mars designed by the European Space Agency. It will explore Mars in search of signs of past and present life. An extensive landing-site selection process is required to find a landing site that is safe from both an engineering perspective and that will help to answer the mission’s science objectives. This research has identified four developments that decrease the efficiency of the current landing-site selection process: 1) there is more and more data available on Mars, which makes combining and analysing all this data manually no longer possible; 2) the technical capabilities of the landing system are increasing, which makes a larger part of the surface available; 3) the questions posed in the scientific and exploration objectives become more and more specific, which sets more stringent requirements on where these questions can be answered; and 4) the Martian surface turned out to be more variable in composition than was previously thought. This study recommends a set of improvements in the form of a decision support system (DSS) that assists experts in the landing-site selection process. The DSS developed for this research includes two prototypes 1) a method that emulates the pattern recognition of a trained, terrain-analysis expert (i.e. a geologist) on a computer, called the terrain fingerprinting method (TFM); and 2) a platform that provides the interface through which all stakeholders in the landing site selection process (scientists, engineers, students, managers) can efficiently interact. This study concludes that I) the TFM can be used to find a landing site that optimises both the safety of the mission and the possibility for scientific return at the site. II) A central platform is required in order to empower the landing site selection community by sharing higher level data products, tools (e.g. TFM software tools), a forum, and documentation. III) The United States Geological Survey (USGS) is the central authority in the planetary sciences community in the USA providing standardisation support, the lack of such a central authority in Europe will negatively affect the process of landing-site selection by European scientists for all future planetary landers. And IV) for the various stakeholders to effectively collaborate and interact in the process of landing-site selection, standardisation of elements related to geographically referenced planetary data is essential.Astrodynamics and Satellite SystemsAerospace Engineerin
Glacial isostatic adjustment model with composite 3-D Earth rheology for Fennoscandia
No full textWe find that sea level data can be explained with our ice model and with information on mantle rheology from laboratory experiments, heatflow and seismology and a pure olivine rheology above 400 km. Moreover, laterally heterogeneous models provide a significantly better fit to relative sea level data than the VM2 viscosity, for our ice model as well as for the ICE-5G model that is based on the VM2 profile. The new ice model gives different constraints on mantle rheology than the ICE-5G model, indicating a possible bias towards mantle viscosity in the latter or shortcomings in our ice model. Present-day uplift rates for a dry rheology are close to GPS observed uplift rate for certain combinations of grain size and temperature fields. Sea level data show a preference for a wet olivine rheology, but in that case uplift rates are too low for all grain sizes and temperature fields. The difficulty to fit sea level data and uplift rate data simultaneously can not be resolved by varying creep parameters below 400 km. Uncertainties in the flow law and the neglect of other materials in the upper mantle, as well as the neglect of flow in the crust could affect our conclusions
Postseismic deformation following the 1997 Umbria-Marche (Italy) moderate normal faulting earthquakes
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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
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