1,720,961 research outputs found
Imagerie d'ombre des satellites géostationnaires
No full textThe submetric characterisation of objects in geostationary orbit is a key challenge for space surveillance, but it is a very ambitious objective at the limits of the resources currently being developed for astronomy. This work focuses on shadow imaging, a method that could potentially address this need through occultations. When a satellite passes in front of a star, it casts a shadow on the ground that encodes the geometric shape of the satellite. This shadow is then collected using small telescopes.To extract the information of interest, we need to digitally combine the measurements from the different telescopes by solving an inverse problem. The aim was first to study the light propagation model in order to validate the concept of the method and to specify and optimise the detector parameters. Then, the objective was to design the inversion algorithm and to estimate the performance of the overall imaging system.This work accurately quantified the atmospheric effects and found them to be relatively small. In addition, simple dimensioning rules were established based on a modal description of diffraction. A multispectral inversion algorithm was proposed and validated on realistic simulations, showing that sub-metric resolutions were indeed achievable. The suggested approach led to a significant simplification of the instrument and an improvement of the reconstructions. Finally, an experimental bench was developed to reproduce diffraction on a small scale under conditions equivalent to shadow imaging. This allowed the inversion to be validated on real data, thus confirming the technique's robustness.La caractérisation submétrique des objets en orbite géostationnaire est un enjeu crucial pour la surveillance de l'espace mais constitue un objectif très ambitieux, à la limite de performance des moyens en cours de développement pour l'astronomie. Ce travail porte sur l'imagerie d'ombre, une méthode permettant de répondre simplement à ce besoin en exploitant des occultations. Lorsqu'un satellite passe devant une étoile, il projette au sol une ombre qui encode la forme géométrique du satellite. Cette ombre est collectée à l'aide de petits télescopes.Pour extraire l'information d'intérêt, il faut combiner numériquement les mesures issues des divers télescopes en résolvant un problème inverse. L'objectif a d'abord été d'étudier le modèle de propagation de la lumière, afin de valider le principe de la méthode et de dimensionner et optimiser les paramètres du detecteur. Puis de concevoir l'algorithme d'inversion et estimer les performances du système d'imagerie global.Ce travail a permis de quantifier précisément les effets atmosphériques qui se sont avérés faibles. De plus, des règles de dimensionnement simples ont été établies à partir d'une description modale de la diffraction. Un algorithme d'inversion multispectral a été proposé et validé sur des simulations réalistes montrant que des résolutions submétriques étaient effectivement atteignables.L'inversion proposée a simplifié l'instrument et amélioré les reconstructions. Enfin, un banc experimental reproduisant à petite échelle la diffraction a été réalisé dans des conditions équivalentes à celle de l'imagerie d'ombre. Il a permis de valider l'inversion sur des données réelles et de prouver ainsi la robustesse de la technique
Imagerie d'ombre des satellites géostationnaires
No full textThe submetric characterisation of objects in geostationary orbit is a key challenge for space surveillance, but it is a very ambitious objective at the limits of the resources currently being developed for astronomy. This work focuses on shadow imaging, a method that could potentially address this need through occultations. When a satellite passes in front of a star, it casts a shadow on the ground that encodes the geometric shape of the satellite. This shadow is then collected using small telescopes.To extract the information of interest, we need to digitally combine the measurements from the different telescopes by solving an inverse problem. The aim was first to study the light propagation model in order to validate the concept of the method and to specify and optimise the detector parameters. Then, the objective was to design the inversion algorithm and to estimate the performance of the overall imaging system.This work accurately quantified the atmospheric effects and found them to be relatively small. In addition, simple dimensioning rules were established based on a modal description of diffraction. A multispectral inversion algorithm was proposed and validated on realistic simulations, showing that sub-metric resolutions were indeed achievable. The suggested approach led to a significant simplification of the instrument and an improvement of the reconstructions. Finally, an experimental bench was developed to reproduce diffraction on a small scale under conditions equivalent to shadow imaging. This allowed the inversion to be validated on real data, thus confirming the technique's robustness.La caractérisation submétrique des objets en orbite géostationnaire est un enjeu crucial pour la surveillance de l'espace mais constitue un objectif très ambitieux, à la limite de performance des moyens en cours de développement pour l'astronomie. Ce travail porte sur l'imagerie d'ombre, une méthode permettant de répondre simplement à ce besoin en exploitant des occultations. Lorsqu'un satellite passe devant une étoile, il projette au sol une ombre qui encode la forme géométrique du satellite. Cette ombre est collectée à l'aide de petits télescopes.Pour extraire l'information d'intérêt, il faut combiner numériquement les mesures issues des divers télescopes en résolvant un problème inverse. L'objectif a d'abord été d'étudier le modèle de propagation de la lumière, afin de valider le principe de la méthode et de dimensionner et optimiser les paramètres du detecteur. Puis de concevoir l'algorithme d'inversion et estimer les performances du système d'imagerie global.Ce travail a permis de quantifier précisément les effets atmosphériques qui se sont avérés faibles. De plus, des règles de dimensionnement simples ont été établies à partir d'une description modale de la diffraction. Un algorithme d'inversion multispectral a été proposé et validé sur des simulations réalistes montrant que des résolutions submétriques étaient effectivement atteignables.L'inversion proposée a simplifié l'instrument et amélioré les reconstructions. Enfin, un banc experimental reproduisant à petite échelle la diffraction a été réalisé dans des conditions équivalentes à celle de l'imagerie d'ombre. Il a permis de valider l'inversion sur des données réelles et de prouver ainsi la robustesse de la technique
Imagerie d'ombre des satellites géostationnaires
No full textLa caractérisation submétrique des objets en orbite géostationnaire est un enjeu crucial pour la surveillance de l'espace mais constitue un objectif très ambitieux, à la limite de performance des moyens en cours de développement pour l'astronomie. Ce travail porte sur l'imagerie d'ombre, une méthode permettant de répondre simplement à ce besoin en exploitant des occultations. Lorsqu'un satellite passe devant une étoile, il projette au sol une ombre qui encode la forme géométrique du satellite. Cette ombre est collectée à l'aide de petits télescopes.Pour extraire l'information d'intérêt, il faut combiner numériquement les mesures issues des divers télescopes en résolvant un problème inverse. L'objectif a d'abord été d'étudier le modèle de propagation de la lumière, afin de valider le principe de la méthode et de dimensionner et optimiser les paramètres du detecteur. Puis de concevoir l'algorithme d'inversion et estimer les performances du système d'imagerie global.Ce travail a permis de quantifier précisément les effets atmosphériques qui se sont avérés faibles. De plus, des règles de dimensionnement simples ont été établies à partir d'une description modale de la diffraction. Un algorithme d'inversion multispectral a été proposé et validé sur des simulations réalistes montrant que des résolutions submétriques étaient effectivement atteignables.L'inversion proposée a simplifié l'instrument et amélioré les reconstructions. Enfin, un banc experimental reproduisant à petite échelle la diffraction a été réalisé dans des conditions équivalentes à celle de l'imagerie d'ombre. Il a permis de valider l'inversion sur des données réelles et de prouver ainsi la robustesse de la technique.The submetric characterisation of objects in geostationary orbit is a key challenge for space surveillance, but it is a very ambitious objective at the limits of the resources currently being developed for astronomy. This work focuses on shadow imaging, a method that could potentially address this need through occultations. When a satellite passes in front of a star, it casts a shadow on the ground that encodes the geometric shape of the satellite. This shadow is then collected using small telescopes.To extract the information of interest, we need to digitally combine the measurements from the different telescopes by solving an inverse problem. The aim was first to study the light propagation model in order to validate the concept of the method and to specify and optimise the detector parameters. Then, the objective was to design the inversion algorithm and to estimate the performance of the overall imaging system.This work accurately quantified the atmospheric effects and found them to be relatively small. In addition, simple dimensioning rules were established based on a modal description of diffraction. A multispectral inversion algorithm was proposed and validated on realistic simulations, showing that sub-metric resolutions were indeed achievable. The suggested approach led to a significant simplification of the instrument and an improvement of the reconstructions. Finally, an experimental bench was developed to reproduce diffraction on a small scale under conditions equivalent to shadow imaging. This allowed the inversion to be validated on real data, thus confirming the technique's robustness
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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