1,720,976 research outputs found
Design and optimization of a low-weight baffle for the laser altimeter BELA on board the ESA BepiColombo mission
Get PDFLAUREA SPECIALISTICAThis dissertation concerns the design and the optimization, from a thermal point of view, of a protective baffle for the transmitter part of the BepiColombo Laser Altimeter (BELA), which will operate in the Mercury’s orbit.
The peculiar characteristics of the environment, in particular the short distance from the Sun and the presence of harmful agents, such as charged particles and strong UV and V-UV radiation, lead to the necessity of protecting the instrument from the environment. An optical filter has been implemented to reject the planetary fluxes, whereas a protective baffle must be designed to reject the solar radiation. Two different designs were candidates for this task: a cylindrical tube and a complex Stavroudis shape, which makes use of ellipsoids and hyperboloids.
The properties of the environment have been analyzed, determining the maximal and minimal radiation for each position of Mercury in its orbit around the Sun and for each position of the satellite around the orbit. The peaks of radiation, and the maximal / minimal values averaged along one orbit, have been determined for the planetary IR radiation, for the albedo and for the direct solar fluxes, defining the thermal worst cases the s/c will experience.
The possible treatments and coatings that can be applied to the two designs of the baffle have been investigated, focusing on the thermo-optical properties and the effect of their degradation under the expected environmental conditions. A campaign of tests has been carried out in situ to determine the effects of some thermal and mechanical treatments on titanium samples, representative of the cylindrical baffle.
A brief introduction to the general thermal problem is then presented, describing the Lumped Parameter method and the software used for the radiative analysis and the solution of the thermal network: ESARAD and ESATAN. A method to implement wavelength-dependant thermo-optical properties has been introduced.
Finally, the thermal models of the two versions of the baffle are illustrated, and the results from the thermal analyses presented. The two concepts have been analyzed comparing the thermal requirements of the unit and the indexes of performance. These indexes include the rejection efficiency, the heat fluxes dumped to the s/c and inside the instrument, the maximal temperatures of baffle and filter
Thermal model and analysis of the BELA transmitter Stavroudis baffle in Mercury orbit
Get PDFIn the frame of the ESA BepiColombo mission to the planet Mercury the German Aerospace Center (DLR), in cooperation with the University of Bern, is designing the first European laser altimeter for planetary exploration (BELA).
While orbiting Mercury the solar flux reaches 14 kW and strikes on the instrument at angles of > 38 deg from the instrument line of sight. The planet surface reaches 700 K while the view factor with the instrument aperture is high due to the low orbit altitude.
Under these conditions a major challenge is the design of the instrument baffles, which shall avoid direct sunlight to reach the optics, minimize the heat load to the instrument and the S/C cavity and reduce stray light.
We describe the thermal model of the transmitter baffle, focusing on advanced features like the approximation of ellipsoids and hyperboloids in the geometrical mathematical model, its optimization with respect to computational time and baffle efficiency, the dynamic implementation of wavelength dependant thermo- optical properties for the calculation of both absorbed planetary fluxes – as function of Mercury surface temperature – and radiative conductances (GR).
The worst cases selection in the scenario of the whole Mercury orbit about the sun is also presented followed by a detailed overview of the analysis results
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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