Stéphane Barre

The Halogenated Metabolism of Brown Algae (Phaeophyta), Its Biological Importance and Its Environmental Significance

Brown algae represent a major component of littoral and sublittoral zones in temperate and subtropical ecosystems. An essential adaptive feature of this independent eukaryotic lineage is the ability to couple oxidative reactions resulting from exposure to sunlight and air with the halogenations of various substrates, thereby addressing various biotic and abiotic stresses i.e., defense against predators, tissue repair, holdfast adhesion, and protection against reactive species generated by oxidative processes. Whereas marine organisms mainly make use of bromine to increase the biological activity of secondary metabolites, some orders of brown algae such as Laminariales have also developed a striking capability to accumulate and to use iodine in physiological adaptations to stress. We review selected aspects of the halogenated metabolism of macrophytic brown algae in the light of the most recent results, which point toward novel functions for iodide accumulation in kelps and the importance of bromination in cell wall modifications and adhesion properties of brown algal propagules. The importance of halogen speciation processes ranges from microbiology to biogeochemistry, through enzymology, cellular biology and ecotoxicology.

X-ray attenuation measurements in a cavitating mixing layer for instantaneous two-dimensional void ratio determination

The purpose of this experimental study was to analyze a two-dimensional cavitating shear layer. The global aim of this work was to obtain a better understanding and modeling of cavitation phenomenon in a 2D turbulent sheared flow which can be considered as quite representative of cavitating rocket engine turbopomp inducers. This 2D mixing layer flow provided us a well documented test case which can be used for the characterization of the cavitation effects in sheared flows. The development of a velocity gradient was observed inside a liquid water flow: Kelvin-Helmholtz instabilities developed at the interface. Vaporizations and implosions of cavitating structures inside the vortices were observed. X-ray attenuation measurements were performed to estimate the amount of vapor present inside the mixing area. Instantaneous two-dimensional void ratio fields were acquired. The real spatial resolutions are 0.5 mm with 2000 fps and 1.5 mm with 20 000 fps. The effective time resolution is equal to the camera frame...

Experimental study of a supersonic jet-mixing layer interaction

An experimental study is performed to analyze the interaction between a control jet (CJ) and a moderately supersonic main jet. Flow visualizations and laser Doppler velocimetry methods are used. A strong instability of the CJ has been identified. The dynamic of this instability corresponds to that of the local mixing layer. Two stability scenarios are proposed, one corresponding to the local Kelvin–Helmholtz instability of the main jet, the other linked to a local absolute instability of the interaction. The impact on the turbulent quantities is analyzed. It is shown that a strong modification of the Reynolds stress is manifest but that this extends only a small distance from the interaction.

Marine Natural Products from New Caledonia—A Review

Marine micro- and macroorganisms are well known to produce metabolites with high biotechnological potential. Nearly 40 years of systematic prospecting all around the New Caledonia archipelago and several successive research programs have uncovered new chemical leads from benthic and planktonic organisms. After species identification, biological and/or pharmaceutical analyses are performed on marine organisms to assess their bioactivities. A total of 3582 genera, 1107 families and 9372 species have been surveyed and more than 350 novel molecular structures have been identified. Along with their bioactivities that hold promise for therapeutic applications, most of these molecules are also potentially useful for cosmetics and food biotechnology. This review highlights the tremendous marine diversity in New Caledonia, and offers an outline of the vast possibilities for natural products, especially in the interest of pursuing collaborative fundamental research programs and developing local biotechnology programs.

Experimental investigation of draft tube flow instability

The draft tube of a hydraulic turbine is the component where the flow exiting the runner is decelerated, thereby converting the excess of kinetic energy into static pressure. However, in some refurbishment cases, the installation of an upgraded runner with an old draft- tube leads to an undesirable efficiency drop as the discharge is increased above the best efficiency point value. It is found to be related to a corresponding sudden variation in the draft tube pressure recovery coefficient at the same discharge. The model of a recent refurbishment which presents this instability is installed in the CREMHyG test rig. Steady and unsteady measurements of velocity and pressure fields of the complex and highly turbulent swirling flow exiting the runner have been carried out at CREMHyG (Grenoble). They included the three components of the velocity. The flow in the draft tube is rich in secondary flows and possible flow separation due to the elbow as well as to the divergent shape of this geometry. Pressure and velocity field measurements in the draft-tube have been performed. They let us identify some phenomena that may explain the origin of the unusual behavior of the draft tube. Finally, the same model, with a modified draft tube geometry that was designed to reduce the efficiency drop phenomenon has been installed. Velocity measurements were made to validate the benefit of such geometry modification.

Dynamic Localization of Vapor Fraction in Turbo Pump Inducers by X-Ray Tomography

An experimental study of the instantaneous local behavior of cavitation in turbo-pump inducers is presented in this article. Experiments held on a hydrodynamic facility equipped with an Ariane 5 inducer permitted achieving the aim. Cavitation is attained by reducing the pressure in a turbo machine having an inducer rotating at 4000 rpm. An X-ray tomography system developed specially for this aim, was used to measure the cavitation. The system employed an industrial X-ray generator and scintillation detectors. The generator/detectors system was fixed while the inducer was rotating. Vapor fraction was determined instantaneously, which confirms the applicability and the precision of the method in such type of measurements despite the constraints imposed by the geometry and the rotation speed. The dense composition of the system components introduced difficulties in the measurement especially at the inducer axis. However, prior information concerning the vapor regime as well as its stationary behavior in certain time intervals helped overcome this problem. Consequently a quantitative and qualitative evaluation of the vapor fraction is obtained. Results show a cavitation regime mostly synchronous with the rotation of the inducer thus permitting the use of tomographic reconstruction for the localization of vapor in the machine. An algebraic reconstruction algorithm (ML-EM) was used to achieve image reconstruction.