ÉTUDE SUR L'ACTIVITÉ DE LA RIBONUCLÉASE PANCRÉATIQUE BOVINE. APPLICATION D'UNE MÉTHODE DE MESURE AU DOSAGE D'UN FACTEUR INHIBITEUR DE LA RIBONUCLÉASE ALCALINE PRÉSENT DANS DES EXTRAITS CELLULAIRES DE FOIE DE RAT

International audienc

New experimental procedure to determine the recombination rate constants between Nitroxides and Macroradicals

A new experimental procedure for the determination of the recombination rate constant, kc, between a propagating macroradical and a nitroxide is proposed. It is based on a single pulse−pulsed lamp polymerization where the main chain growth breaking event between two consecutive pulses is the recombination of the macroradicals with the nitroxide. The recovered polymer is analyzed by size exclusion chromatography, and the parameters of the molar mass distribution are used to determine kc, in a similar way as that traditionally applied in the determination of the chain transfer rate constants, i.e., the Mayo method using the number- or weight-average degrees of polymerization and the full chain length distribution method. We named the technique RNR−PLP−SEC for radical nitroxide recombination−pulsed lamp polymerization−size exclusion chromatography. The particular polystyryl macroradical−SG1 nitroxide system was tested to validate it. To apply a consistency check, the experimental parameters have been varied according to the recommendations made by the IUPAC for the measurements of the propagation rate constants via PLP. The recombination rate constant kc was measured over a temperature range where no cleavage of the formed alkoxyamine might occur. At 40 °C kc = 2.6 × 105 L mol-1 s-1, and the value increased from 1.1 × 105 L mol-1 s-1 at 15 °C to 4.0 × 105 L mol-1 s-1 at 82 °C. The extrapolation at 120 °C led to 5.3 × 105 L mol-1 s-1, in good agreement with the values already reported in the literature

Buried sandbodies within present-day estuaries (Atlantic coast of France) revealed by very high resolution seismic surveys

International audienc

Role of tidal range and coastline morphology on the evolution of two macrotidal sand spits

International audienceAbstract The present study examines the stratigraphy of two sandspits that both appeared and developed since the middle of the 17th century during the Little Ice Age. The Arçay spit is located along the macrotidal Atlantic coast in South‐West France with a maximum tidal range of 6.5 m. The Pointe du Banc in the English Channel, North‐West France, is located in a hypertidal coastal setting with a tidal range of up to 14 m. The evolution of the two spit systems has been compared using historical maps, ground penetrating radar data and facies analysis and geochronological data from sediment cores. The Pointe du Banc spit developed between 1650 and 1750 CE, in a dominant seaward direction while the main mode of construction of the Arçay spit was in a longshore direction. It is proposed that this difference relates to sediment supply and coastline morphology. At the Pointe du Banc spit, the large tidal range causes a long wind fetch and sustained aeolian sediment supply. Moreover, the spit is located at the apex of a large‐scale embayment where sediment transport from north and south converges. Combined, these factors result in a positive sediment budget and seaward shoreline progradation. At the Arçay spit, high wave obliquity results in a large littoral drift and sustained longshore spit construction. At both locations, low gradient shorefaces may have favoured a net landward‐directed sediment flux that supply sand to the foreshore

Evolution de flèches sableuses depuis le Petit Age Glaciaire. Forçage climatique et contrôle tidal

National audienc

Sandspit evolution in macrotidal settings, a comparative study

International audienc

Sandspit evolution in macrotidal settings, a comparative study.

International audienc