In-lab ALOHA mid-infrared up-conversion interferometer in the photon counting regime @λ = 3.39 µm

International audienceAstronomical Light Optical Hybrid Analysis ([email protected] µm) is a new instrumental concept designed for high angular resolution astronomical imaging in the L Band. The originality of our experimental device is to include a frequency conversion process in each arm of the interferometer that frequency shifts the mid infrared signal to the near infrared domain. This method relaxes the stringent limitations due to the thermal noise background radiated by the instrument itself. The aim of this paper is to estimate the current sensitivity limit of the instrument and validate the ability to provide calibrated contrasts with a quasi monochromatic signal. We demonstrate the possibility to measure fringe contrasts greater than 94.5% with a signal-to-noise ratio close to 7. The flux level at the input of each arm of the interferometer is then equal to 100 fW. This would correspond to a zero magnitude star in the L Band for a 1 m 2 telescope surface and a 3 nm converted spectral bandwidth

Multichannel spectral mode of the ALOHA up-conversion interferometer

International audienceIn this paper, we propose a multichannel spectral configuration of the Astronomical Light Optical Hybrid Analysis (ALOHA) instrument dedicated to high resolution imaging. A frequency conversion process is implemented in each arm of an interferometer to transfer the astronomical light to a shorter wavelength domain. Exploiting the spectral selectivity of this non-linear optical process, we propose to use a set of independent pump lasers in order to simultaneously study multiple spectral channels. This principle is experimentally demonstrated with a dual-channel configuration as a proof-of-principle

Induction of Phlorotannins and Gene Expression in the Brown Macroalga Fucus vesiculosus in Response to the Herbivore Littorina littorea

Mechanisms related to the induction of phlorotannin biosynthesis in marine brown algae remain poorly known. Several studies undertaken on fucoid species have shown that phlorotannins accumulate in the algae for several days or weeks after being exposed to grazing, and this is measured by direct quantification of soluble phenolic compounds. In order to investigate earlier inducible responses involved in phlorotannin metabolism, Fucus vesiculosus was studied between 6 and 72 h of grazing by the sea snail Littorina littorea. In this study, the quantification of soluble phenolic compounds was complemented by a Quantitative real-time PCR (qRT-PCR) approach applied on genes that are potentially involved in either the phlorotannin metabolism or stress responses. Soluble phlorotannin levels remained stable during the kinetics and increased significantly only after 12 h in the presence of grazers, compared to the control, before decreasing to the initial steady state for the rest of the kinetics. Under grazing conditions, the expression of vbpo, cyp450 and ast6 genes was upregulated, respectively, at 6 h, 12 h and 24 h, and cyp450 gene was downregulated after 72 h. Interestingly, the pksIII gene involved in the synthesis of phloroglucinol was overexpressed under grazing conditions after 24 h and 72 h. This study supports the hypothesis that phlorotannins are able to provide an inducible chemical defense under grazing activity, which is regulated at different stages of the stress response

In Silico Survey of the Mitochondrial Protein Uptake and Maturation Systems in the Brown Alga Ectocarpus siliculosus

The acquisition of mitochondria was a key event in eukaryote evolution. The aim of this study was to identify homologues of the components of the mitochondrial protein import machinery in the brown alga Ectocarpus and to use this information to investigate the evolutionary history of this fundamental cellular process. Detailed searches were carried out both for components of the protein import system and for related peptidases. Comparative and phylogenetic analyses were used to investigate the evolution of mitochondrial proteins during eukaryote diversification. Key observations include phylogenetic evidence for very ancient origins for many protein import components (Tim21, Tim50, for example) and indications of differences between the outer membrane receptors that recognize the mitochondrial targeting signals, suggesting replacement, rearrangement and/or emergence of new components across the major eukaryotic lineages. Overall, the mitochondrial protein import components analysed in this study confirmed a high level of conservation during evolution, indicating that most are derived from very ancient, ancestral proteins. Several of the protein import components identified in Ectocarpus, such as Tim21, Tim50 and metaxin, have also been found in other stramenopiles and this study suggests an early origin during the evolution of the eukaryotes

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

Etude du mécanisme d'importation des ARN de transfert dans les mitochondries de plantes

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Co-phasing of a diluted aperture synthesis instrument for direct imaging: Experimental demonstration on a temporal hypertelescope

International audienceContext. The diluted aperture synthesis is one of the most promising ways of obtaining direct images with an angular resolution in the milliarcsecond range. By applying apodization techniques to a hypertelescope, it is possible to discriminate between objects with a high contrast in intensity with a reasonable number of telescopes (<10). Aims. To reach such performances, we attempt to develop a co-phasing system capable of stabilizing the optical path differences with an accuracy better than λ/100 RMS. Methods. We propose a method based on a joint use of a sub-aperture piston phase-diversity technique and a genetic algorithm to co-phase a laboratory prototype called a temporal hypertelescope (THT). First, we simulated the behavior of this instrument and inferred the related statistical properties of our co-phasing method. In a second step, we implemented this co-phasing system on our THT prototype. Results. We obtain an experimental stabilization of the optical path differences of about λ/300 RMS over 1000 s. Thanks to this result, we are able to acquire an image of a high-contrast binary system. We also validate that the instrument accurately estimates the object characteristics, i.e. 25 μrad for the angular separation and ΔH = 9.1 magnitude difference between the main star and its companion