1,721,022 research outputs found
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
Uncertainty analysis in lattice physics calculations: application of the NRG's TALYS evaluated data to a case of burnup
Full text linkTENDL evaluate files have been processed with NJOY and different libraries have been created and processed by the deterministic code DRAGON. The aim of this process is obtain hundreds of burnups calculation that has been used to evaluate the uncertainty using the Monte Carlo approach. TENDL library have been analyzed and compared with other libraries (as JENDL or SCALE). Finally, results for the most important isotopes (235U, 238U, 239Pu) for the PWR Burnup Pin-Cell Benchmark UAM-I are presented using this method.Outgoin
Uncertainty analysis in lattice physics calculations: application of the NRG's TALYS evaluated data to a case of burnup
No full textTENDL evaluate files have been processed with NJOY and different libraries have been created and processed by the deterministic code DRAGON. The aim of this process is obtain hundreds of burnups calculation that has been used to evaluate the uncertainty using the Monte Carlo approach. TENDL library have been analyzed and compared with other libraries (as JENDL or SCALE). Finally, results for the most important isotopes (235U, 238U, 239Pu) for the PWR Burnup Pin-Cell Benchmark UAM-I are presented using this method.Outgoin
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
SIBYL - Scaling Incertitudes BY modeLing
No full textLes domaines d'application des codes de transport de neutrons de Monte Carlo (MC) sont en croissance constante. Leurs capacités de simuler pratiquement toutes les géométries en mode énergie continue sont de moins en moins contraintes par les incertitudes statistiques de leurs sorties, grâce à la réduction des coûts de calcul. De plus, de vastes champs d'applications ont récemment été ouverts après l’introduction de sensibilités dans les MC statiques. L'utilisation de ces sensibilités ouvre des nouvelles possibilités pour les outils de physique des réacteurs, qu'il s'agisse du couplage neutronique et thermo-hydraulique ou de l'évaluation de la stabilisation ou de l'incertitude des calculs de l'évolution du combustible. Ces évolutions sont associées à un renouvellement complet de la démarche face aux incertitudes. Auparavant, l’analyse d’incertitude était effectuée avec les sensibilités étant calculées après les calculs principaux. Si les sensibilités et les incertitudes sont calculées comme un point clé de la procédure de couplage, à l'avenir, les incertitudes seront disponibles lors de la conception des nouveaux itinéraires.Les codes déterministes étaient autrefois la seule voie permettant de calculer les sensibilités sur la base de la théorie des perturbations développée dans les années 70, qui est l’un des ingrédients de l’analyse d’incertitude. Il est utilisé de manière intensive, en particulier pour l'analyse de l'incertitude des données nucléaires lorsque les incertitudes sont présentées sous la forme de matrices de covariance. Un premier contrat entre l'ILL et le LPSC vise à utiliser ces sensibilités pour évaluer les incertitudes des paramètres de sécurité au début du cycle.Le projet s'appuiera sur deux activités complémentaires:La première activité sera consacrée au calcul de l’évolution des paramètres de sécurité et de performance (évolution du flux neutronique dans les tubes à faisceau) et des incertitudes associées. En raison de la combustion relativement faible des combustibles de type ILL, les contributions du 239Pu aux fissions, puis la modification des paramètres les plus importants (par exemple, la fraction de neutrons retardés effective) devraient être relativement faibles, même en fin de cycle. Néanmoins, ces impacts seront probablement mesurables. Ils doivent être évalués avec précision pour la démonstration de la sûreté, même si l’impact sur le fonctionnement du réacteur doit être limité.La deuxième activité sera la réalisation de l’expérience de physique du réacteur lors des tests physiques des procédures de démarrage du réacteur. La quantification de l'incertitude n'est qu'un aspect de la validation des outils de simulation. Les expériences resteront obligatoires dans le cadre de la démonstration de sécurité. Pendant la durée de la thèse, certaines barres de commande devraient être remplacées par des barres en hafnium. Nous proposons de contribuer aux tests associés à la validation de ces nouveaux dispositifs et éventuellement de suggérer des tests supplémentaires. Plusieurs contacts avec le CEA et d'autres groupes du CNRS ont clairement montré qu'il existe un intérêt commun fort à utiliser le réacteur ILL en tant que test pour certains paramètres dynamiques du réacteur (keff, durée de vie des neutrons, etc.), sur la base de paramètres de mesure innovants en utilisant la théorie du bruit neutronique. Parmi les nouvelles capacités des outils de simulation utilisés et développés dans la première partie, certains développements contribueront à la cohésion entre les deux parties.Monte Carlo (MC) neutron transport codes application fields are growing constantly. Their capacities to simulate virtually any geometry in continuous energy mode are less and less constrained by the statistical uncertainties of their outputs, thanks to the reduction of computing costs. Furthermore, large fields of applications have been recently opened after the spread of the availability of sensitivities in static MC [1]. The use of those sensitivities opens very innovative possibilities for reactor physics tools, whether for the coupling of neutronics and thermal-hydraulics [2] or for the stabilization or uncertainty evaluation of fuel evolution calculations [3,4]. These developments are associated with a complete renewal of the approach for uncertainties. Uncertainty analysis used to be done a posteriori, as the sensitivities where calculated after the main calculations. If the sensitivities and uncertainties are calculated as a key point of the coupling procedure, in the future, the uncertainties will be available by design of the new routes.Deterministic codes used to be the only route able to calculate sensitivities on the base of Perturbation Theory developed in the 70’s, which is one of the ingredients of uncertainty analysis. It is used intensively, in particular for nuclear data uncertainty analysis when the uncertainties are given in the form of covariance matrices. A first contract between ILL and LPSC aims at using those sensitivities for the evaluation of uncertainties of safety parameters at Beginning of Cycle.The project will rely on two complementary activities:The first activity will be devoted to the calculation of the evolution of the safety and performance (neutron flux evolution in beam tubes) parameters and of the associated uncertainties. Because of the relatively low burn up of ILL fuels, 239Pu contributions to fissions and then the change in the most important parameters (for instance the effective delayed neutron fraction) are expected to be relatively low even at end of cycle. Nevertheless, these impacts will probably be measurable. They must be assessed accurately for safety demonstration even if the impact for the reactor’s operation should be limited.The second activity will be the realization of reactor’s physics experiment during the physical tests of reactor’s startup procedures. Uncertainty quantification is only one aspect of validation of simulation tools. Experiments will remain mandatory as part of the safety demonstration. During the time of the PhD, some control rods should be changed for Hafnium ones. We propose to contribute to the tests associated with the validation of those new devices and maybe to suggest additional tests. Several contacts with CEA and other groups of CNRS clearly showed that there is actually a strong, common interest for using ILL reactor as a test case for some reactor dynamics parameters (âeff, neutron lifetimes etc…), on the basis of innovative measurement set-ups using neutron noise theory. Among the new capacities of the simulation tools used and developed in the first part, some developments will contribute to the cohesion between the two parts
Uncertainties evaluation methods on an industrial core calculation chain
No full textLes REPs constituent la filière de réacteurs nucléaires la plus répandue dans le monde : EDF en exploite 58 en France, et s'intéresse donc tout particulièrement à l'amélioration constante de leur sûreté et de leurs performances. Les codes de calcul jouent un rôle important dans l'évaluation de la sûreté nucléaire. La conception et l'exploitation sûres des réacteurs reposent sur des outils de simulation numérique. Ces derniers répondent entre autres, aux exigences de sureté pour le démarrage et l’exploitation des réacteurs nucléaires et permettent la mise en place de nouveaux concepts. Il est donc très important de disposer d’outils de calcul performants, vérifiés, validés et qualifiés.Pour réaliser ses études de modélisation du comportement du cœur, EDF utilise un ensemble de codes de calculs déterministes rassemblés dans la chaine de calcul coeur CASSIOPEE. Les calculs des section efficaces au niveau assemblage sont réalisées avec le Générateur Automatique de Bibliothèques GAB qui appelle le code réseau APOLLO2. Le code COCCINELLE utilise les résultats de GAB pour les simulations au niveau cœur.Des paramètres de fonctionnement et de constitution du cœur (géométrie, plans de chargement, réflecteurs radial et axiaux…), et des données (neutronique, thermohydraulique…) sont nécessaires en complément des schémas de calcul. Les résultats obtenus sont comparés avec des mesures réalisées sur le parc en exploitation.Il existe un besoin de mieux caractériser les sources incertitudes associées aux paramètres de sortie de la chaîne de calcul cœur, par exemple, ceux qui sont mesurés lors des essais physiques de démarrage et en cours de cycle. À travers le Rétour d'EXperience du Parc, des paramètres de modèles sont ajustés afin de minimiser ces écarts calculs/mesures.L'établissement des marges d’exploitation est alors effectué à partir de calculs conservatifs. Ceux-ci tiennent compte de l’état de connaissance des écarts pesant sur ces paramètres et des conditions réelles d’exploitation. Cela oblige à prendre des provisions : par exemple, à sûreté égale, plus l'incertitude est élevée, plus le domaine de fonctionnement est réduit.REPs are the most widespread nuclear reactor industry in the world: EDF operates 58 in France, and is therefore particularly interested in constantly improving their safety and performance. Computer codes play an important role in the assessment of nuclear safety. The safe design and operation of reactors is based on digital simulation tools. These meet, among other things, the safety requirements for the start-up and operation of nuclear reactors and allow the implementation of new concepts. It is therefore very important to have efficient, verified, validated and qualified calculation tools.To carry out its core behavior modeling studies, EDF uses a set of deterministic calculation codes brought together in the CASSIOPEE core calculation chain. The calculations of the cross sections at the assembly level are carried out with the Automatic Generator of Libraries GAB which calls the cell code APOLLO2. The COCCINELLE code uses the results of GAB for simulations at the core level.Core parameters (geometry, loading planes, radial and axial reflectors, etc.), and data (neutronics, thermohydraulics, etc.) are required in addition to the calculation diagrams. The results obtained are compared with measurements taken from the feedback operation.There is a need to better characterize the sources of uncertainties associated with the output parameters of the core computation chain, for example, those which are measured during the physical start-up tests and during the cycle. Through the Park Experience Feedback, model parameters are adjusted in order to minimize these calculation / measurement deviations.The operation margins are established on the basis of conservative calculations. These take into account the state of knowledge of the deviations weighing on these parameters and the actual operating conditions. This makes it necessary to take provisions: for example, with equal safety, the higher the uncertainty, the smaller the operating range
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
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