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International audience; Given the high eruption recurrence in the Michoacán-Guanajuato volcanic field (MGVF) in central Mexico, the birth of a new monogenetic volcano can be expected in the future. It is important, therefore, to reconstruct the past eruptions of its many different volcanoes, including estimates of lava flow emplacement times and their rheological properties. These studies define the range of possible future eruptive scenarios and are necessary to evaluate potential risk. The Rancho Seco monogenetic volcano, located in the central part of the MGVF (19°37′03”N, 101°28′21”W), was radiocarbon-dated at ~27,845 years BP. Its eruption initiated with a violent-Strombolian phase that produced a scoria cone and was followed by the effusion of at least seven associated andesitic lava flows, reflecting drastic changes in the eruptive dynamics. Effusive activity probably involved decreases in the magma ascent and discharge rates linked to efficient degassing in an open system. Lava chemical composition suggest an origin of partial melting of a subduction-modified hydrated heterogenous mantle wedge and textural and mineralogical analysis indicates significant crystal fractionation and minor assimilation of granodioritic basement rocks. High-resolution LiDAR imagery was used to estimate lava flow viscosities and emplacement times by following a morphology-based methodology. Results indicate that lava flow viscosities ranged from 105 to 109 Pa·s and emplacement durations between 32 and 465 days for the flow units considered (F5 and F6). The entire eruption may have lasted from 2 to 6 years with a mean effusion rate of 4 to 15 m3/s. Our results are also pertinent to archaeologists studying the architectural remains of Angamuco, a large urban pre-Hispanic site built on Rancho Seco's lava flows.

Alluvial paleosol–sedimentary sequences containing animal fossils, and paleobotanical and paleopedological archives have a potential for reconstructing Quaternary paleoenvironments in Southern Mexico and for understanding the paleoecology of Pleistocene megafauna. In the section of Axamilpa river four pedostratigraphic units were recognized. The lower Gleyic and Vertic pedological Units are at the end of marine isotopic stage (MIS) 3 while the upper Humic and (most probably) Calcic Units correspond to MIS 2 according to the radiocarbon dates of humus. The micromorphological analysis indicates an incipient development and syn-sedimentary character of paleopedogenesis in the periodically water-saturated environment (indicated by redoximorphic features, hydrogenic carbonates and low values of magnetic susceptibility in most strata). The δ 13 C values of the paleosol humus range from − 22.6 to − 24.7, indicating a C3 vegetation, whereas in the modern soil it is higher (− 15.2) pointing to an abundance of the C4 and CAM plants. The δ 13 C signature of the vegetation inferred from the teeth enamel of the fossil fauna appeared to be less negative than that of humus from corresponding paleosols. The alimentary preferences of the paleofauna which fed on grasses with high proportion of C4 plants explain this difference. The phytolith analysis shows dominance in conifer forms, followed by C4 and C3 grasses. The content of conifer phytoliths is progressively reduced towards the top of the sequence. We interpret the Late Pleistocene landscape of this area as a heterogeneous forest–grassland landscape with the forest shrinking through time and the grass areas increasing. Swampy floodplain meadows (inferred from paleopedological results) could provide a habitat for grassy vegetation. Both isotope and phytolith records demonstrate a contrasting difference between Pleistocene and recent vegetation dominated by xerophytic shrubs and succulents. This vegetation change could play important role in the extinction of Pleistocene megafauna.

International audience; The changes in the optical properties of Au/TiO2 powder catalyst, prepared by the deposition-precipitation method, are measured in the visible range by use of a home-made diffuse differential reflectance spectrometer, when the ambient atmosphere is switched between H2 and O2. Two main features are observed: (i) a short wavelength one, located between 400 and 600 nm, is shown to be related to the modifications of the plasmon resonance of the 3-dimensional metallic gold particles with mean size around 4 nm, induced by the exposure to oxygen or by its removal; (ii) a second feature, observed at long wavelengths between 600 and 1100 nm, is extremely sensitive to the exposure to oxygen. This optical feature could be due to the presence in the catalyst, either of Au0 clusters of several tens atoms, which are expected to display molecular-like transitions in this optical range, or to specific sites of the Au particles (edge atoms or peripheral atoms at the interface with the TiO2 support), which could be highly reactive to oxygen.

We consider the nonlinear Schrodinger equation i ψ t = − ψ x x ± 2 cos 2 x | ψ | 2 ψ , x ∈ S 1 , t ∈ R and we prove that the solution of this equation, with small initial datum ψ ( 0 , x ) = e ( A exp ( i x ) + B exp ( − i x ) ) , will periodically exchange energy between the Fourier modes e i x and e − i x as soon as A 2 ≠ B 2 . This beating effect is described up to time of order e − 5 / 2 while the frequency is of order e 2 . We also discuss some generalizations.

International audience; Esta comunicación en el seminario “Pensar la emancipación desde el espacio social” buscaintercambiar nuestra experiencia de investigadores y profesores comprometidos en unaperspectiva crítica y radical así como seguir el trabajo reflexivo iniciado sobre nuestraimplicación al interior de la institución universitaria. Si queremos insistir sobre los colectivosa los cuales hemos participado con el propósito de realizar este compromiso, no podemosocultar nuestras trayectorias sociales e institucionales que explican, influyen y alimentannuestra perspectiva científica. Ambos estudiantes en doctorado de ciencias sociales sinfinanciamiento (cuyo sujeto de tesis no es tal vez sin vínculo con la ausencia de becainstitucional), hemos experimentado la precariedad y la flexibilidad en el trabajo cuando senecesitó asegurar nuestras condiciones materiales de investigación y de existencia.La primera materialización de nuestro compromiso crítico y radical se produjo durante esteperiodo de trabajo como vigilante en un liceo y después como profesor temporal en launiversidad. Frente a la atomización y a la competencia entre los colegas pero también frentea la indiferencia de las organizaciones sindicales mayoritarias (inscritas en lógicasburocráticas, corporativistas y cogestionarías), hemos participado a la institucionalización decolectivos de asalariados con el fin de crear vínculos colectivos y una fuerza colectiva capazde ejercer un (contra-) poder sobre la estructura de dominación para mejorar nuestrascondiciones de trabajo y de empleo. Esas reivindicaciones inmediatas, e incluso parasolamente hacer cumplir el derecho, no fueron sin embargo separadas de una crítica globalsobre las condiciones estructurales de estos procesos que vivíamos, particularmente larestructuración del Estado en contexto capitalista neoliberal. Esta implicación en las luchassobre nuestros lugares de trabajo se prolongó en la apertura de áreas de investigación sobrelos movimientos sociales y la acción colectiva conflictual así como sobre la reconfiguraciónde las relaciones de clase en las sociedades capitalistas contemporáneas.La organización del Seminario Practica e Idea de la Emancipación con jóvenes investigadoresde sociología y geografía social constituye la segunda materialización de nuestra perspectivacrítica y radical. Frente a la orientación dominante de la universidad, particularmente elreciente giro neoliberal de contratación utilitarista de la investigación, se buscó constituir unproyecto común de reflexión sobre las luchas contemporáneas contra las relaciones dedominación, explotación y alienación con el propósito de producir fisuras en el saberinstituido y de asumir nuestro posicionamiento ideológico dentro de la institución. Elconcepto de emancipación permito federar las distintas sensibilidades ideológicas y políticasde los miembros del colectivo de organización del seminario, colectivo fundado sobre lógicasafinatarias y políticas buscando desarrollar prácticas democráticas en una institución regidapor el corporativismo y el autoritarismo. Con la voluntad de subvertir la lógica encerrada yelitista de la universidad, hemos tratado en cada sesión de asociar sin jerarquizar uninvestigador y un militante. El objetivo de esta apertura del seminario a los activistas era deacentuar la porosidad de las fronteras entre dos campos del mundo social que no se habla paraestablecer diálogos e incluso construir proyectos en común.La reflexión sobre estos dos ejes constituyentes de nuestro compromiso crítico y radicalvislumbra una coherencia en cuanto a nuestra concepción de la emancipación y nos lleva aproponer a la discusión tres conclusiones trasversales. Primero, estimamos que el proceso deemancipación debe vincular de manera necesaria y continua, en un mismo movimientodialectico, las prácticas y las ideas de la emancipación para mantener la unidad de la praxisrevolucionaria. Segundo, la forma del colectivo permite dar vida a los principios de lademocracia directa en la óptica de una coproducción igualitaria de un común abierto eindeterminado. Esta organización asume de manera pragmática la dimensión conflictual de la democracia contra el dogmatismo o el purismo de algunas franjas de los movimientosradicales. Tercero, nuestra concepción de la emancipación postule una articulación necesariay posible de los distintos corrientes y teorías críticos y radicales (feminismo, antirracismo,anticapitalismo, anarquismo, etc.) así como la articulación de reivindicaciones inmediatas dela vida cotidiana y perspectiva global de transformación social. * Source : https://pensarlaemancipacion.files.wordpress.com/2015/10/mathieu-uhel-y-simon-leroulley.pdf (consulté le 18/12/2019)

International audience; Epicentral locations of non-volcanic tremors (NVT) in the Mexican subduction zone are determined from the peak of the energy spatial distribution and examined over time. NVT is found to occur persistently at a distance of ∼215 km from the trench, which we term the "Sweet Spot" because this region probably has the proper conditions (i.e., temperature, pressure, and fluid content) for the NVT to occur with minimum shear slip. High-energy NVT episodes are also observed every few months, extending ∼190 km to ∼220 km from the trench with durations of a few weeks. During the 2006 slow slip event (SSE) the duration and the recurrence rate of the NVT episodes increased. Low-energy episodes were also observed, independent from the high-energy episodes, ∼150 km to ∼190 km from the trench during the 2006 SSE. Both the high and low energy episodes were made up of many individual NVT's that had a range of energy-release-rates. However, the highest energy-release-rates of the high-energy episodes were consistently double those of the low-energy episodes and the persistent activity at the Sweet Spot. We suggest that all of the high-energy episodes are evidence of small, short repeat interval SSE. Given this model, the increased recurrence rate of the high-energy NVT episodes during the 2006 long-term SSE implies that short-term SSE's also increase during the SSE and are therefore triggered by the SSE.

International audience; Diffuse optical reflectance of Au/TiO2 powder catalysts, prepared by the deposition-precipitation method, is measured in the UV-visible range in controlled atmosphere. An intense optical absorption observed around 550 nm is interpreted by the excitation of plasmon resonances in the 4 nm gold nanoparticles (NPs). The location, intensity, and width of the absorption can be reproduced theoretically by using a distribution of shapes of the NPs. The changes of the reflectance upon exposure of the Au/TiO2 catalyst to different atmospheres (O2/He, H2/He, CO/He) are measured in real-time by use of a homemade differential diffuse reflectance (DDR) spectrometer. The derivative-like DDR spectrum shows that the exposure to oxygen leads to the adsorption of oxygen species at the surface of the Au NPs. By modeling the DDR spectrum, we analyze different possible processes that could occur during the oxygen exposure and we find that the main effect is a charge transfer from gold to the adsorbed oxygen species, combined with a slight flattening of the Au NPs. The exposure to CO gives a similar but much smaller effect than the one of oxygen. Finally, real-time optical measurements performed during the exposures to oxygen indicate that two different sets of particles are probably present in the catalyst, and react with different kinetics, slightly flat three-dimensional NPs and very flat almost two-dimensional NPs.

International audience; In order to assess the physical mechanisms at stake when giant gas bubbles burst at the top of a magma conduit, laboratory experiments have been performed. An overpressurized gas cavity is initially closed by a thin liquid film, which suddenly bursts. The acoustic signal produced by the bursting is investigated. The key result is that the amplitude and energy of the acoustic signal strongly depend on the film rupture time. As the rupture time is uncontrolled in the experiments and in the field, the measurement of the acoustic excess pressure in the atmosphere, alone, cannot provide any information on the overpressure inside the bubble before explosion. This could explain the low energy partitioning between infrasound, seismic and explosive dynamics often observed on volcanoes.

"En México, los terópodos son un grupo de dinosaurios poco conocido, el escaso material descrito ha sido referido solamente a nivel de "familia". Como resultado de la investigación paleontológica realizada en el Estado de Coahuila, se recuperó material dental de terópodos. Se identificaron los géneros Saurornitholestes, cf. Troodon, así como Tyrannosauridae y un terópodo indeterminado. La composición faunística de terópodos es similar a la descrita en el Parque Nacional del Big Bend, Texas, confirmando la existencia de la zona biogeográfica de dinosaurios del sur de las Grandes Planicies de América del Norte. De confirmarse la presencia de Troodon en estas latitudes sugeriría que la distribución geográfica de este género de terópodo era mucho más amplia de lo supuesto anteriormente."

International audience; It is shown lhat lhe decahedral recursive model (DRM) explains at atomic level the structure of the decagonal (0) phase and associated approximant structures as random coincidence networks (RCNS), random packings of clusters satisfying DRM energy minimizing rules. RCNS are degenerate random tilings that become quasiperiodic when entropic disorder is maximized at high tempmure through phason flips requiring small atomic movements. Such phason flips can change lhe relative ratio and geometry of tiles, making transformations between systems using differenl tile sets possible. Electron microscopic obreNations for AICuCoSl. AICuFeCr, AlCoCu and AlPdMn systems are reproduced, including the observed Fibonacci sequenced lines in the former.