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Les propriétés radiatives des magmas secs et riches en cristaux
No full textLa température est un paramètre clé contrôlant la rhéologie d’une coulée de lave. Cependant, le comportement imprévisible des éruptions empêche les mesures directes de températures. Par conséquent,ces mesures sont régulièrement effectuées par des techniques de télédétection (avec des détecteurs sur le terrain ou depuis l’espace) développées pour mesurer la radiation Infra-Rouge (IR). Ces techniques bien établies sont malgré tout sujettes à d’importantes erreurs liées au manque de connaissance de l’un des paramètres les plus importants, dénommé l’émissivité spectrale. L’objectif de cette étude est de combler ce manque en explorant la relation émissivité–température de basaltes lato sensu (basalte de Bardarbunga,basanite de Fasnia, MORB basalte de Juan de Fuca, et océanite du Piton de la Fournaise), et de cristaux magmatiques (pyroxène, plagioclase, et oxyde de fer). L’émissivité spectrale a été mesurée de façon in situ à des températures magmatiques (jusqu’à 1800 K) sur une large gamme spectrale (350–8000 cm⁻¹; 1.25–28.6 μm),à l’aide d’un appareil IR sans contact. Pour éclaircir le comportement radiatif complexe de ces échantillons en fonction de la température, des analyses systématiques de la texture, de la composition, de la structure, et du comportement thermique de ceux-ci ont été effectuées à l’aide des MEB, Microsonde, spectroscopie Raman,DRX, MET, et DSC. Les résultats démontrent que l’émissivité spectrale est dépendante de la température, du nombre d’onde, ainsi que du degré de polymérisation combiné à la teneur en FeO. L’émissivité spectrale est grandement influencée par la présence de cristaux qui ont des propriétés radiatives distinctes et plus particulièrement par l’agglomération et la cristallisation à l’échelle microscopique d’oxydes riche en Fe. Dès lors, cette étude prouve que l’émissivité spectrale pour une composition magmatique donnée ne peut pas être considérée comme constante. Pour finir, les mesures de laboratoire sur l’émissivité spectrale permettent de raffiner de 50 degrés la valeur de température de la coulée de lave d’Holuhraun (2014–2015) initialement mesurée par télédétection. Ces nouvelles connaissances pourront permettre dans le futur de réduire l’erreur associée aux estimations de température faites par télédétection IR, cette dernière étant indispensable pour l’amélioration de l’évaluation des risques lors d’une crise volcanique.Temperature is a key parameter controlling the rheology of lava flows. However, the unpredictable hazard of eruptions prevents direct measurements of hot magmatic bodies. Thus, the temperature of lava is mostly retrieved by remote sensing techniques (ground- or satellite-based detectors) build on measuring infrared (IR) radiance. These well-established techniques are however subjected to important errors related to the poor knowledge of one of the most critical parameters, namely spectral emissivity. The aim of this study is to fill this gap by exploring the emissivity–temperature relationship of different basalts lato sensu (Bardarbungabasalt, Fasnia basanite, Juan de Fuca MORB basalt, and Oceanite from Piton de la Fournaise) and magmatic minerals (pyroxene, plagioclase, iron-rich oxide). In situ emissivity measurements were performed at magmatic temperatures (up to 1800 K) over a wide spectral range (350–8000 cm⁻¹; 1.25–28.6 μm), using a non-contact IR apparatus. To unravel the complex radiative behavior of the samples with temperature, structural, chemical,textural, and thermal analyses using SEM, EMPA Raman spectroscopy, XRD, TEM, and DSC, were systematically performed. Results show that spectral emissivity varies with temperature, wavenumber, and the sample degree of polymerization combined with FeO content. Spectral emissivity is greatly affected by the presence of crystals with distinct radiative properties and specifically by the clustering and crystallization of Fe-rich crystals at the micro-scale. Consequently, this study proves that spectral emissivity cannot be assumed constant for a given magma composition. Finally, laboratory-measured values of spectral emissivity allowed refining the remote sensing temperature of the 2014–2015 Holuhraun lava by ~50 degrees. These new insights will ultimately reduce uncertainties in temperature estimates based on IR technology, information that are crucial to improve hazard assessment in volcanic crisis
Rôle macroscopique des interfaces solide-liquide et liquide-gaz sur l'interaction eau-roche en milieu poreux
No full textDans l'étude des interactions eau-roche, l’aire de surface des interfaces est un point d’attention depuis longtemps pour les géochimistes, mais la réactivité locale le long des interfaces joue également un rôle important. Généralement, on considère que les propriétés volumiques des phases en interaction décrit bien les forces motrices macroscopiques et le transfert de masse résultant. Cependant, les observations directes sur le terrain des transitions de phase ont remis en cause ce classicisme, avec de claires indications que la taille des pores, la distance à l’interface solide, ou bien la présence d'une interface liquide-air incurvée, peuvent entraîner les transitions de phase sur des voies réactionnelles inattendues. Deux types d'expériences ont été menées, l’une à l'échelle de l'interface, principalement centrée sur l’interface eau-solide, et l’autre à l'échelle du pore, tournée vers l'influence de ponts capillaires sur la géochimie intra-porale. Tout d'abord, des mesures de micro-spectroscopie infrarouge aux interfaces, utilisant un micro-faisceau (source laser et synchrotron) et un microscope confocal, ont été réalisées sur une cavité micrométrique fermée (inclusion fluide) pour explorer la variation de l'énergie vibratoire de l'eau en fonction de la distance à l’interface solide. Les données hyperspectrales ont affiché une signature dépendant de la distance pour l'eau sur une épaisseur de 1 ± 0,5 μm en lien avec l’état de surface du solide (effet hydrophobe) et des énergies de surface résultantes. La conversion de la signature spectrale près de l’interface du quartz en énergie libre de Gibbs conduit à une signature de surface de 600 J/mol à température ambiante (22°C) et de 1000 J/mol à plus haute température (155°C). Ce potentiel chimique croissant modifie évidemment la réactivité le long d'une telle interface solide-liquide, et affecte une quantité importante d'eau. Il en ressort que les interactions eau-roche dans les pores, les canaux et les cavités doivent tenir compte de la chimie de surface des minéraux et pas seulement de leur composition, de leur forme ou de leur taille. Deuxièmement, la variation de réactivité dans un réseau de pores est étroitement liée à la présence (ou non) de ponts capillaires liquide-air et à leur intensité capillaire. Nous avons exploité des puces nanofluidiques pour y établir un état capillaire contrôlé en ajustant l'humidité relative. Le phénomène de cavitation de l'eau et la cinétique de l'évaporation capillaire tenant compte de la forme des pores montrent les relations de cause à effet entre l'humidité relative et l'effet capillaire. Ces mesures remettent en question l'utilisation systématique des données macroscopiques sur les phases volumiques pour évaluer et prédire comment les interactions eau-roche se produisent et évoluent avec le temps dans les milieux poreux, en particulier dans les aquifères non saturés en eau.In water-rock interaction, the surface area of interfaces has received long-term attention from geochemists, but local reactivity along interfaces also plays a significant role. The general statement is that using the bulk properties of interacting phases describes the macroscopic driving forces and the resulting mass balances. However, direct field observations challenged classicism, demonstrating that the pore radius, the distance to the solid boundary, or the presence of a curved liquid-air interface can drive the phase transitions along unexpected reactional pathways. This study has targeted two types of experiments to probe what can be the additional parameters involved in the reasoning, one at the interface-scale, mainly focused on the water-solid boundary, and one at the pore-scale, turned to the influence of capillary bridges on thein-pore geochemistry. First, the interface-based infrared micro-spectroscopy measurements, using micro-beam (laser and synchrotron source) and a confocal microscope, were performed on a micrometric closed cavity (fluid inclusion) to explore the variation of the vibrational energy of water as a function of the distance to the solid boundary. The hyperspectral data displayed a distance-dependent signature for water over a 1 ± 0.5 μm thickness (called interphase domain) because of the solid surface property (hydrophobic effect) and the resulting surface energies. The conversion of the spectral signature near the quartz boundary into Gibbs free energy leads to a 600 J/mol surface-imprinting at room temperature (22°C) to1000 J/mol at high temperature (155°C). Consequently, this increasing chemical potential changes the reactivity along such a solid-liquid interface, which affects a significant amount of water. It comes out that the surface chemistry of minerals and not only their composition, shape, or size play a crucial role in water-rock interactions in pores, channels, and cavities. Second, the reactivity variation in a pore network is closely linked to the presence (or not) of liquid-air capillary bridges and their capillary intensity. We exploited nanofluidic chipsets to establish capillarity in a controlled way by tuning the relative humidity, with which we are exploring the water-rock-gases equilibria at various capillary states leading to a phase transition. The water cavitation phenomenon and kinetic of the evaporation concerning the pore shape show the effect of relative humidity on the capillary-driven effect. These measurements question the systematic use of the bulk phases datasets to evaluate and predict how water-rock interactions occur and evolve with time in the porous media, especially in water-unsaturated aquifer
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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