1,721,027 research outputs found
A partially molten mantle
No full textInternational audienceA global analysis of seismic waves has identified a widespread sharp velocity anomaly at the base of the low seismic velocity zone that is consistent with partial melting, closing a decades-long debate about the origin of this zone
Electrical conductivity of hydrous silicate melts: Implications for the bottom-up hydration of Earth's upper mantle
No full textInternational audienceThe upwelling of the hydrous mantle transition zone triggers dehydration-induced partial melting atop the 410-km discontinuity. Here we investigate the electrical conductivity of hydrous silicate melts in the 200-400 km depth range and explore whether melting at the 410-km depths is responsible for the hydration of the upper mantle. Our experimental electrical conductivity data demonstrate that the mantle at 180-350 km depths is mostly melt free, confirming the H 2 O under-saturated conditions. However, the residual mantle from partial melting atop the 410-km discontinuity may contain various possible amounts of water according to the initial mantle transition zone and melt concentrations. This residual H 2 O could contribute to the hydration of the upper mantle either through diffusion or material replacement by upwelling. Our calculations suggest that the diffusion may not be responsible for the hydration of the upper mantle to present H 2 O concentration of 50-200 ppm wt. Melting of the upwelling mantle transition zone with less than 1500 ppm wt. H 2 O produces residual peridotites with ∼ 200 ppm H 2 O at the 410-km discontinuity. Continuous upwelling of such hydrous residues would gradually replace the dry upper mantle with depleted residual hydrous peridotites in less than 260 Ma. In this study, we propose a bottom-up hydration mechanism for the Earth's upper mantle driven by dehydration-melting at the 410-km discontinuity. The hydrous partial melting at the top of the asthenosphere appears to be a consequence of H 2 O saturation in the upwelling residual peridotites
Deformation of olivine-orthopyroxene aggregates at high pressure and temperature: Implications for the seismic properties of the asthenosphere
No full textCo-auteur étrangerInternational audienc
Viscosity Measurements at High Pressures: A Critical Appraisal of Corrections to Stokes' Law
No full text<p>Included are central data and codes for the manuscript "Viscosity Measurements at High Pressures: A Critical Appraisal of Corrections to Stokes' Law", submitted for review.</p>
Minéral composition and physical properties of the Martian mantle
No full textMars est la seconde planète la plus étudiée après la Terre. Les décennies d’observations et missions spatiales ont permis d’obtenir de nombreuses contraintes sur sa structure telles que la taille de son noyau, son état entièrement liquide ou encore la structure de la croûte Martienne. Les météorites Martiennes (SNC) et les analyses chimiques des basaltes à la surface de la planète permettent également de déterminer la composition chimique de son manteau, qui apparaît être bien plus riche en fer que le manteau Terrestre (Fe# ∈ [0,20 - 0,25]). L’objectif de cette thèse est donc d’étudier expérimentalement la structure, la minéralogie et les profils sismiques de Mars, et plus particulièrement l’effet du fer sur les profils sismiques Martiens. Nous avons alors mesuré les vitesses des ondes ultra sonores à haute pressions(3-17 GPa) et hautes températures (40-1200 °C) grâce à une presse multi-enclumes couplée au rayonement X d’un synchrotron. Nos résultats montrent que lorsque le taux de fer est élevé (Fe#0.27), la ringwoodite apparait à plus basse pression que la wadsleyite et est en équilibre avec l’olivine. Cette transition implique une discontinuité sismique positive à 600 km de profondeur.De plus, lorsque le manteau a une composition si riche en fer, du ferropériclase se forme à partir de 16 GPa, pouvant induire une chute des vitesses des ondes. Les profils sismiques de Mars obtenus grâce à l’inversion des données de la sonde InSight ne présentent ni discontinuité sismique à 600 km de profondeur, ni diminution forte des vitesses proches de 1100 km de profondeur(16 GPa). Ainsi le taux de fer du manteau Martien est probablement proche de Fe#0.20 plutôt que de Fe#0.25. Le second résultat majeur de notre étude est que le profil de température choisi pour modéliser les profils sismiques a une importance majeure, et peut induire les Low Velocity Zone observées dans les profils sismiques Martien de la littérature récente.Mars is the second most studied planet after the Earth. Decades of obser vations and space missions have provided many constraints on its structure such as the size of its core, its entirely liquid state or the structure of the Martian crust. Martian meteorites (SNC) and chemical analyses of basalts on the surface of the planet also allow to determine the chemical composition of its mantle, which appears to be much richer in iron than the terrestrial mantle (Fe# E [0.20 - 0.25]). The objective of this thesis is therefore to study experimentally the structure, mineralogy and seismic profiles of Mars, with a focus on the impact of iron on the Martian seismic profiles. To do so, we measured the velocities of ultrasonic waves at high pressures (3-17 GPa) and high temperatures (40-1200 °C) using a multi-anvil apparatus coupled within a synchrotron facility. Our results show that when the iron content is high (Fe#0.27), ringwoodite appears at lower pressure than wadsleyite and is in equilibrium with olivine. This transition implies a positive seismic discontinuity at 600 km depth. Moreover, when the mantle is rich in iron, feropericlase is formed at 16 GPa, which can induce a velocity drop. The seismic profiles of Mars obtained from the inversion of the InSight data do not show any seismic discontinuity at 600 km depth, nor a strong decrease in velocities near 1100 km depth (16 GPa). Thus the iron content of the Martian mantle is probably closer to Fe0.20 rather than Fe0.25. The second major result of our study is that the temperature profile chosen to model the seismic profiles has a major impact, and can induce the low velocity zone observed in the Martian seismic profiles of the recent literature
Viscosity Measurements at High Pressures: A Critical Appraisal of Corrections to Stokes' Law
No full text<p>Included are central data and codes for the manuscript "Viscosity Measurements at High Pressures: A Critical Appraisal of Corrections to Stokes' Law", published May 2, 2024.</p>
<p>Reference for full article:</p>
<p>Ashley, A.W., Mookherjee, M., Xu, M., Yu, T., Manthilake, G., & Wang, Y. (2024). Viscosity measurements at high pressures: A critical appraisal of corrections to Stokes' Law. Journal of Geophysical Research: Solid Earth, 129, e2023JB028489. https://doi.org/10.1029/2023JB028489</p>
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
- …
