1,721,043 research outputs found
Modélisation des nuages de dioxyde de carbone (CO2) sur Mars : application aux nuages mésosphériques.
No full textCarbon dioxide (CO2) ice clouds on Mars stem from the condensation of the main atmospheric component (95% CO2). Numerous theoretical studies suggest that these clouds may have an influence on Mars' current climate, and that they have played a significant role in its past evolution. Only recently, observational constraints on crystal sizes and opacities of these clouds have been obtained after their discovery in the mesosphere. In this context, we have focused on the modeling of these clouds, with the aim of characterizing the microphysics of a near-pure vapor condensing in a rarefied atmosphere. We have developed a growth rate model for crystals, taking into account the potentially high temperature difference between the crystal surface and the environment, which appears to be important for a near-pure vapor. A one dimensional microphysical model has then been developed for these clouds to simulate their formation in the mesosphere. Thanks to this model, we can now explain their short lifetime and their diurnal behavior. We show that it is possible to reproduce the cloud crystal sizes, but not their opacities, as long as clouds are supposed to form onto dust particles (regolith) lifted from the ground by storms. A meteoritic input has been used to simulate denser clouds, in agreement with observations. The new microphysical model is intended to be coupled to Mars' climate and meteorological models.Les nuages de cristaux CO2 sur Mars sont issus de la condensation du constituant majoritaire de l'atmosphère (95% de CO2). De nombreuses études théoriques suggèrent que ces nuages pourraient avoir une influence sur le climat martien actuel et qu'ils ont sans doute joué un rôle significatif au cours de son évolution passée. Seulement récemment, des contraintes précises sur la taille des cristaux qui les composent et leur opacité ont été obtenues après leur découverte dans la mésosphère. C'est dans ce cadre que nous nous sommes intéressés à la modélisation de ces nuages avec pour ambition de caractériser la microphysique de condensation d'un gaz majoritaire dans une atmosphère raréfiée. Nous avons mis au point un modèle de croissance des cristaux tenant compte de la différence de température entre la surface du cristal et son environnement, différence qui s'avère importante dans le cas d'une vapeur majoritaire. Un modèle de microphysique de ces nuages à une dimension a été ensuite développé pour simuler leur formation dans la mésosphère. Grâce à ce modèle, nous sommes maintenant en mesure d'expliquer les faibles durées de vie ces nuages ainsi que leur comportement diurne. Nous montrons qu'il est possible de reproduire la taille de leurs cristaux, mais pas leur opacité tant que ceux-ci sont supposés se former à partir des particules minérales issues du régolite. Des scénarios d'apport exogène de noyaux de condensation ont été étudiés et ont permis de simuler des nuages plus denses conformes aux observables. Ce nouveau modèle de microphysique est appelé à rejoindre des modèles de climat et de météorologie martiens actuellement en développement
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
Evidence of Meteor Smoke Particles as precursors for formation of mesospheric clouds on Mars
No full textInternational audienceMesospheric clouds have been systematically observed in the Martian mesosphere for about a decade. Not all of the observations allow for the cloud composition to be defined. However, several observations have revealed clouds formed of CO2 ice crystals, although in some cases a water ice composition has been detected as well. The condensation of the main component of the atmosphere is a fairly unique phenomenon. Although the lower atmosphere of Mars is very dusty and rich in ice nuclei, the mesosphere should be fairly devoid of dust lifted from lower layers (due to weak probability of lifting to high altitudes and low atmospheric densities favouring sedimentation). A very interesting candidate as a source of ice nuclei in the mesosphere comes from a terrestrial analogue. Meteor Smoke Particles have been shown to play a role in the formation of the mesospheric clouds on the Earth, and in a recent modelling study we have been able to show that an exogenous source of ice nuclei is required in the Martian mesosphere to be able to model clouds with observed properties. We will present a short review of observations and a summary of the cloud properties, and then discuss the model results pointing towards Meteor Smoke Particles as a necessary ingredient for the formation of mesospheric clouds on Mars
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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