Ice-crystal traces imply ephemeral freezing in early Permian equatorial Pangea

Delicate impressions in lacustrine strata of the lower Permian (lower Cisuralian) Usclas Formation record ephemeral freezing in equatorial Pangea. These sediments accumulated in the paleoequatorial and intramontane Lodève Basin (southern Massif Central, France) during peak icehouse conditions of the Late Paleozoic Ice Age. Experimental replication of these features supports the interpretation that they are ice-crystal molds. Evidence for films of ice in marginal-lacustrine sediment at such low latitudes and inferred low to moderate altitudes (1–2 km) calls for a reevaluation of climate conditions in eastern equatorial Pangea. Ephemeral freezing implies either cold tropical temperatures (~5 °C cooler than the Last Glacial Maximum) and/or lapse rates that exceeded those of the Last Glacial Maximum. Extreme continentality of the Lodève Basin would have amplified seasonality, albeit the climatic forcing(s) necessary to have promoted cold temperatures in equatorial Pangea remain enigmatic

Détermination des sections efficaces différentielles absolues pour les transitions 11 S → 41 S, 41 D, 5 1S et 51 D de l'atome d'hélium

The electron-photon coïncidence method is used for determining absolute differential cross sections for electron impact scattering in helium. Studies have been made for excitation of the 4 1S, 4 1D, 5 1S and 5 1D states which are not resolved by an electron spectrometer ; the experiments were performed for incident energies from 50 to 200 eV and for angles of 5-20°. For excitation of these states, generalised oscillator strengths are obtained from values of differential cross sections.Nous utilisons la méthode des coïncidences électron diffusé-photon émis pour la détermination des sections efficaces différentielles de collisions électrons-atomes d'hélium. Nous étudions quelques transitions qui ne sont pas résolues par analyse électronique : 1 1S →4 1S, 4 1D, 5 1S et 5 1D. Les expériences sont effectuées dans un domaine d'énergie compris entre 50 et 200 eV et pour des angles de diffusion compris entre 5° et 20°. A partir des mesures de sections efficaces différentielles obtenues, nous avons déduit les valeurs de forces d'oscillateurs généralisées pour les transitions étudiées

Triple differential cross section of rare gas atoms in different low energy kinematics

Triple differential cross sections have been measured for the electron-impact ionization of rare gases in two coplanar geometries. Results are presented for 20 eV excess energy with respect to ionization threshold for ionization of helium, neon and argon. These enable us to investigate the target dependence of triple differential cross section angular-distributions. For ionization of helium, we compare our absolute measurements with the convergent close coupling calculations whereas, for ionization of neon and argon, the comparison is made with the distorted wave Born approximation calculations. Additional measurements carried out on argon near threshold are also presented

Effect of Incorporation of Boron Nitride Nanoparticles on Oxygen Barrier Properties of Poly (3-hydroxybutyrate-co-3-hydroxyvalerate)

International audienc

Structure formation of poly(ether-imide) films using non-solvent vapor induced phase separation: relationship between mass transfer and relative humidity

International audienc

Modulating Viscoelastic Properties of Physically Crosslinked Self-Assembled Gelatin Hydrogels through Optimized Solvent Conditions

International audienc

Quantitative PVP mapping in PVDF hollow fiber membranes by using Raman spectroscopy coupled with spectral chemiometrics analysis

Fabrication of fouling resistant UF membranes requires the use of hydrophilic polymer additives that must be trapped in the polymer matrix during the phase separation processing. The knowledge of the polymeric additive distribution across the whole thickness should help to the design of more efficient membranes. This paper aims at developing a new methodology based on Raman microscopy spectroscopy owing to its high spatial resolution. A UF hollow fiber made from a blend of PVDF as polymer matrix and PVP as additive was chosen as a model membrane for this study. The PVP concentration profile along the cross-section radial axis was determined by using two ways of spectrum treatment including the analytical method by the peak intensity ratio calculation and a multivariate analysis with a partial least-squares regression model. The feasibility of the two approaches was discussed