33 research outputs found
Colloids and suspended particulate matters influence on Ni availability in surface waters of impacted ultramafic systems in Brazil
Artificially induced migration of redox layers in a coastal sediment from the Northern Adriatic
Long-term experimental studies suggest that, under transient anoxic conditions, redox fronts within the sediment shift upwards, causing sequential rise and fall of benthic fluxes of reduced species (Mn(II), Fe(II) and S(-II)). Infaunal benthic organisms are associated with different redox fronts as micro-habitats and must be affected by such changes during natural hypoxia events. In order to document the geochemical evolution of the sediment during prolonged anoxia in the framework of an in situ experiment designed to
mimic natural conditions, benthic chambers were deployed on the seafloor of the Northern Adriatic and sampled after 9, 30 and 315 days of incubation. Oxygen and sulfide were measured continuously in the early stages (9 days) of the experiment.
High-resolution pore water profiles were sampled by DET probes and redox-sensitive species (S(VI), Mn(II)and Fe(II)) and alkalinity were measured. Starting oxygen saturation was about 80% within the chamber. After 7 days, anoxia was established in the bottom waters within the chambers. Mn(II) and Fe(II) started diffusing towards the anoxic water column until they reached the surficial sediment. Being reoxidized there, Mn and Fe reprecipitated, giving a rusty coloration to the seafloor. Infaunal species appeared at the sediment surface. After 20 days, all macro-organisms were dead. Decomposition of macroorganisms at the sediment–water interface generated S(-II) within the entire height of the chamber, leading to a downward flux of sulfides into the sediment, where they were quickly oxidized by metallic oxides or precipitated as FeS. S(-II) was below detection in the water column and pore waters at the end of the experiment. Our results suggest that S(-II) enrichment in the water column of coastal systems, which are episodically anoxic, is strongly controlled by the biomass of benthic macrofauna and its decay during anoxia, whereas its residence time in the water column is controlled by iron
availability (as solid oxides or as dissolved reduced cations) within the sediment, even without water circulation
Factors affecting the onset of deoxyribonucleic acid synthesis during wheat embryo germination. Study of the changes in DNA polymerases A, B and C and the pool of DNA precursors
Utilisation d'une couche isolante ferroélectrique (PZT) pour l'amélioration des transistors MISFET organiques
Le travail présenté concerne la réalisation de transistors à effet de champ MISFET à couche active d'oligomères de sexithiophène (6T). Dans cette étude, nous utilisons comme isolant un film
ferroéléctrique : le Pb(Zr,Ti)O3 (PZT). La permittivité élevée du matériau montre une amélioration des performances (diminution des tensions de fonctionnement d'un ordre de grandeur,
augmentation de la transconductance) et permet d'envisager un effet mémoire