1,720,968 research outputs found
Ballon pathfinders for ultra-high energy cosmic ray detection from space : optics performance and search for air showers
No full textLes Rayons Cosmiques d'Ultra Haute Énergie (RCUHE) sont des particules chargées venant de l'espace avec des énergies >1018 eV jusqu'à une énergie mesurée de 3×1020 eV. Ils sont les messagers cosmiques les plus énergétiques, cependant leur origine et les mécanismes permettant leur accélération restent inconnus. Leur observation est difficile à cause de leur très faible flux (1 particule par stéradian par km2 par siècle) et nécessite des techniques de détection indirectes, utilisant l'atmosphère comme un calorimètre. Le projet JEM-EUSO a pour but le développement d'un télescope spatial capable d'observer les gerbes atmosphériques produites par les RCUHE par le biais de leur émission de fluorescence en UV (300 - 400 nm). Pour atteindre ces objectifs, deux projets ballons démonstrateurs ont été développés afin de tester la technologie et les méthodes requises: EUSO-Balloon et EUSO-SPB1, qui ont volé en 2014 et 2017 respectivement. Une technologie clé de ces démonstrateurs est leur système d'optique réfractive composé de deux larges lentilles de Fresnel (presque égal à 1 m2). EUSO-Balloon a volé pendant une nuit et son système optique a contribué à l'observation de traces de laser et la mesure du bruit de fond UV. Néanmoins, la performance des optiques est restée mal comprise, i.e. l'efficacité et sa fonction d'étalement du point (PSF). Ce travail explique la méthode utilisée pour caractériser la performance de l'optique et l'efficacité globale des lentilles de Fresnel. La performance mesurée peut être comprise par la combinaison d'un modèle de diffusion semi-empirique avec une simulation classique de tracé de rayon. EUSO-SPB1 a collecté des données pendant 12 nuits. On présente l'analyse des événements enregistrés suite au déclenchement de l'algorithme de "trigger". On classifie ces événements en différentes catégories et on discute leurs caractéristiques. On montre que la majorité des événements enregistrés sont des rayons cosmiques qui interagissent directement avec le détecteur ainsi que des défauts instrumentaux sur les tubes photomultiplicateurs du détecteur. Aucune gerbe atmosphérique n'a été trouvé dans cette analyse.Ultra High Energy Cosmic Rays (UHECR) are charged particles coming from outer space with energies >1018 eV up to a record measured energy of 3 × 1020 eV. They are the most energetic cosmic messengers coming to earth, however their origin and acceleration mechanisms remain a mystery. Their observation is characterized by their low flux (one particle per steradian per km2 per century) requiring indirect detection techniques using the atmosphere as a calorimeter. The JEM-EUSO framework aims at developing a space-borne telescope to observe the UHECR induced atmospheric particle cascades (air showers) through their UV fluorescence emission (300 - 400 nm). To validate JEM-EUSO's technology and methods, two balloon-borne pathfinders have been developed: EUSO-Balloon and EUSO-SPB1, they were flown in 2014 and 2017 respectively. One of the key technologies of these pathfinders is their refractive optical system consisting of two large aspherical Fresnel lenses (almost equal to 1 m2). EUSO-Balloon flew during one night and it's Fresnel optics contributed to the observation of laser tracks in the atmosphere and the measurement of the UV night-time emission. However, the performance of the optics remained misunderstood i.e. the efficiency and the point spread function. This work describes the method used to characterize the optics performance and global efficiency of the Fresnel lenses of EUSO-Balloon. The measured performance of the optics can be understood as the combination of a semi-empirical diffusion model with a classic ray tracing simulation. EUSO-SPB1 took data during 12 nights until the termination of the mission. We present an analysis of events found in triggered data while searching for air showers. We classify these events into different populations whose characteristics and origins we discuss. We show that the majority of our triggered events are direct cosmic ray interactions on the detector as well as instrumental features of the photo-multipliers. No air shower candidate was found in the analysis
First light of the EUSO-Balloon telescope : toward the detection of ultra-high energy cosmic rays from space
No full textLes rayons cosmiques ont été découverts il y a un siècle par Victor Hess à bord d'un vol scientifique en ballon. La physique des rayons cosmiques et les ballons stratosphériques ont partagé depuis lors une histoire commune, que ce soit pour d'authentiques découvertes ou en utilisant les ballons comme plateformes de test technologique pour de nouvelles missions satellites. Cette thèse, développée au sein de la collaboration JEM-EUSO, traite d'un démonstrateur en ballon stratosphérique. Notre but scientifique final est l'étude des Rayons Cosmiques de Ultra-Haute Energie (RCUHE), les particules les plus énergétiques connues dans l'Univers. Les RCUHES ont des énergies macroscopiques de plus de 10^20eV mais étant extrêmement rares, leurs origines sont encore inconnues. Ces derniers pénètrent notre atmosphère à une fréquence de un par km2 par siècle, produisant une gerbe atmosphérique géante, détectable notamment par la lumière de fluorescence ultraviolette qu'elle émet. Le principe de détection proposé par notre collaboration consiste dans l'utilisation d'un observatoire spatial, JEM-EUSO. Son objectif est d'observer un très grand volume d'atmosphère afin d'enregistrer un nombre significatif des événements ultra-violet de fluorescence initiés par les RCUHEs. Le démonstrateur EUSO-Ballon a été développé par la collaboration JEM-EUSO dans le but de démontrer les technologies et méthodes utilisées par le futur instrument spatial. Le 25 août 2014, EUSO-Ballon a été lâché depuis la base de ballons stratosphériques de Timmins (Ontario, Canada) par la division ballon du CNES. L'instrument a fonctionné pendant toute une nuit astronomique, observant depuis 38km d'altitude la lumière UV provenant de divers types de sols et de centaines de gerbes atmosphériques simulées. Ces dernières ont été produites par des flashers et un laser embarqués dans un hélicoptère volant sous EUSO-Ballon pendant deux heures. Ces résultats ont été rendus possibles par la restitution de l'attitude de l'instrument effectuée à l'IRAP, c'est-à-dire une analyse exhaustive des données du vol des différents appareils de mesure d'attitude de la nacelle du ballon. Une caractérisation précise de chaque sous-système était aussi indispensable à l'exploitation des données du vol. Le système optique innovant, composé de deux grandes lentilles de Fresnel, a été intégré et entièrement testé à l'IRAP. Face au large système réfractif de l'instrument, une nouvelle méthodologie de test a été développée. Les performances de l'optique, efficacité et spot focal, ont ainsi été mesurées et se sont révélées étonnamment différentes des prédictions des modèles numériques. Ces mesures sont utilisées pour l'analyse des données du premier vol et pour mieux comprendre le comportement de ces toutes nouvelles optiques, éléments clés dans la conception de l'instrument JEM-EUSO.A century ago Cosmic Rays were discovered by Victor Hess during one of the very first scientific balloon flights. Ever since, Cosmic Ray physics and stratospheric balloons have shared a common history - either through genuine discoveries or by using balloon platforms as technology test beds for new satellite missions. This thesis, carried out within the JEM-EUSO collaboration, is about such a pathfinder balloon mission. Our ultimate science goal is the study of Ultra-High Energy Cosmic Rays (UHECR), the most energetic particles known in the Universe. Having macroscopic energies of over 10^20 eV, UHECRs are of yet unknown cosmic origin and are extremely rare. They penetrate our atmosphere at a rate of about one event per km2 and century, producing energetic atmospheric air showers, detectable through the ultraviolet fluorescence light they emit. The technique that our collaboration proposes for their detection consists of a spaceborne observatory, JEM-EUSO. Its objective is to monitor a very large volume of the Earth's nighttime atmosphere from above, recording a significant sample of ultraviolet light tracks initiated by UHECRs. In order to demonstrate the technologies and methods featured in the future space instrument, the EUSO-Balloon pathfinder has been developed by the JEM-EUSO collaboration. On August 25, 2014, EUSO-Balloon was launched from Timmins Stratospheric Balloon Base (Ontario, Canada) by the balloon division of the French Space Agency CNES. From a float altitude of 38 km, the instrument operated during the entire astronomical night, observing UV-light from a variety of groundcovers and from hundreds of simulated air showers, produced by flashers and a laser during a two-hour helicopter under-flight. These results have been made possible by the restitution of the instruments attitude carried out at IRAP, i.e. an exhaustive analysis of the flight data from various attitude sensors on board of the balloon gondola. Also, a precise understanding of the Fresnel optics was required to analyze the data of the first EUSO-balloon flight. The all new optical system, integrated and tested at IRAP, has been characterized during two measurement campaigns. To test this large refractive system, a new test method has been developed. The optics performance, i.e. the efficiency and point spread function, came as something of a surprise, since none of the numerical models had predicted the observed behavior. These measurements are used in the analysis of the flight data and for the deep understanding of these brand-new Fresnel optics, key element in the design of the JEM-EUSO instrument
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
Focusing Telescopes in Nuclear Astrophysics
No full textThis volume is the first of its kind on focusing gamma-ray telescopes. Forty-eight refereed papers provide a comprehensive overview of the scientific potential and technical challenges of this nascent tool for nuclear astrophysics. The book features articles dealing with pivotal technologies such as grazing incident mirrors, multilayer coatings, Laue- and Fresnel-lenses - and even an optic using the curvature of space-time. The volume also presents an overview of detectors matching the ambitious objectives of gamma ray optics, and facilities for operating such systems on the ground and in space. The extraordinary scientific potential of focusing gamma-ray telescopes for the study of the most powerful sources and the most violent events in the Universe is emphasized in a series of introductory articles. Practicing professionals, and students interested in experimental high-energy astrophysics, will find this book a useful referenc
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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