Akinetes and ancient DNA reveal toxic cyanobacterial recurrences and their potential for resurrection in a 6700-year-old core from a eutrophic lake

International audienc

Effects of oil exposure and dispersant use upon environmental adaptation performance and fitness in the European sea bass, Dicentrarchus labrax.

International audienceThe worldwide increasing recourse to chemical dispersants to deal with oil spills in marine coastal ecosystems is a controversial issue. Yet, there exists no adequate methodology that can provide reliable predictions of how oil and dispersant-treated oil can affect relevant organism or population-level performance. The primary objective of the present study was to examine and compare the effects of exposure to untreated oil (weathered Arabian light crude oil), chemically dispersed oil (Finasol, TOTAL-Fluides) or dispersant alone, upon the ability of fish for environmental adaptation. To reach that goal, we implemented high-throughput, non-lethal challenge tests to estimate individual hypoxia and heat tolerance as surrogate measures of their capacity to face natural contingencies. Experimental populations were then transferred into semi-natural tidal ponds and correlates of individuals' fitness (growth and survival) were monitored over a period of 6 months. In accordance with our stated objectives, the contamination conditions tested corresponded to those observed under an oil slick drifting in shallow waters. Our results revealed that the response of control fish to both challenges was variable among individuals and temporally stable (repeatable) over a 2-month period. Exposure to chemical dispersant did not affect the repeatability of fish performance. However, exposure to oil or to a mixture of oil plus dispersant affected the repeatability of individuals' responses to the experimental challenge tests. At population level, no difference between contamination treatments was observed in the distribution of individual responses to the hypoxia and temperature challenge tests. Moreover, no correlation between hypoxia tolerance and heat tolerance was noticed. During the field experiment, hypoxia tolerance and heat tolerance were found to be determinants of survivorship. Moreover, experimental groups exposed to oil or to dispersant-treated oil displayed significantly lower survival than control or dispersant-exposed groups. Finally, from the four experimental populations tested, the one exposed to chemically dispersed oil presented the lowest growth rate

Deep-sea versus shallow conditions: a comparative ecobarotoxicological study

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Growth and immune system performance to assess the effect of dispersed oil on juvenile sea bass (Dicentrarchus labrax)

International audienc

Optical and structural characterization of femtosecond laser written micro-structures in germanate glass

Abstract We report on direct femtosecond laser writing in zinc barium gallo-germanate glasses. A combination of spectroscopic techniques allows to progress in the understanding of the mechanisms taking place depending on the energy. In the first regime (type I, isotropic local index change) up to 0.5 µJ, the main occurrence is the generation of charge traps inspected by luminescence, together with separation of charges detected by polarized second harmonic generation measurements. At higher pulse energies notably at the threshold corresponding to 0.8 µJ or in the second regime (type II modifications corresponding to nanograting formation energy domain), the main occurrence is a chemical change and re-organization of the network evidenced by the appearance of molecular O2 seen in the Raman spectra. In addition, the polarization dependence of the second harmonic generation in type II indicates that the organization of nanogratings may be perturbed by the laser-imprinted electric field

Towards second-harmonic generation micropatterning of glass surface

Thermal poling of sodium borophosphate niobium glasses, previously coated with a thin silver layer micropatterned by femtosecond laser irradiation, is demonstrated. The field-assisted ion-exchange process for fabricating planar surface in this glass substrate is analyzed. Inside the silver ablated lines obtained by femtosecond laser irradiation, we clearly observe a change in the distribution of the frozen electrostatic field that is modulated by the Ag+/Na+ ion-exchange process during the thermal poling

Accurate second harmonic generation microimprinting in glassy oxide materials

Spatial and geometry controls of second order optical properties at the micrometer scale have been achieved on borophosphate niobium glasses by thermal poling using micropatterned anode electrodes. Electrode structuring should induce local field enhancement, which is observed at the edges of an indium tin oxide-ablated layer. A lateral poling effect governs the geometry and the strength of the electric field implemented. The potential of such process to fabricate large scale microstructured periodical design of second order optical properties has been demonstrated.Initiative d'excellence de l'Université de Bordeau

Accurate second harmonic generation microimprinting in glassy oxide materials

Spatial and geometry controls of second order optical properties at the micrometer scale have been achieved on borophosphate niobium glasses by thermal poling using micropatterned anode electrodes. Electrode structuring should induce local field enhancement, which is observed at the edges of an indium tin oxide-ablated layer. A lateral poling effect governs the geometry and the strength of the electric field implemented. The potential of such process to fabricate large scale microstructured periodical design of second order optical properties has been demonstrated.Initiative d'excellence de l'Université de Bordeau

Crystalline / glass nanoscale chemical separation induced by femtosecond laser pulses in aluminosilicate glass

International audienceAn aluminosilicate glass with a molar composition of 60%Al$_2$O$_3$–40%SiO$_2$ fabricated by the aerodynamic levitation technique was irradiated in volume using an infrared femtosecond laser. Optical retardance was observed and measured upon a wide range of varying laser parameters including pulse energy, repetition rate, pulse duration, writing speed, and laser polarization. A similar analysis was performed in silica glass (Suprasil CG) taken as a reference. We measured retardance values as high as 100 nm in the aluminosilicate glass, which is approximately 2x higher than previously investigated aluminosilicate glasses. Raman spectroscopy and electron microscopy techniques revealed the presence of an orientable lamellar structure, commonly referred to as nanogratings, composed of alternate SiO$_2$-enriched amorphous layers with Al$_2$O$_3$-enriched ones. The latter are essentially crystallized in a 3Al$_2$O$_3$:2SiO$_2$ Mullite phase. This internal structuring, the first one in a congruent glass, brings additional insights into the mechanisms leading to nanogratings formation, and may be proved useful for future glass-based functional optical devices with very large thermal stability