Accurate measurement of Cn2 profile with Shack-Hartmann data

The precise reconstruction of the turbulent volume is a key point in the development of new-generation Adaptive Optics systems. We propose a new Cn2 profilometry method named CO-SLIDAR (COupled Slope and scIntillation Detection And Ranging), that uses correlations of slopes and scintillation indexes recorded on a Shack-Hartmann from two separated stars. CO-SLIDAR leads to an accurate Cn2 retrieval for both low and high altitude layers. Here, we present an end-to-end simulation of the Cn2 profile measurement. Two Shack-Hartmann geometries are considered. The detection noises are taken into account and a method to subtract the bias is proposed. Results are compared to Cn2 profiles obtained from correlations of slopes only or correlations of scintillation indexes only.Comment: 10 pages, 8 figures, SPIE Conference "Astronomical Telescopes and Instrumentation" 2012, Amsterdam, paper 8447-19

Structural Variations in Hybrid All-Nanoparticle Gibbsite Nanoplatelet/Cellulose Nanocrystal Multilayered Films

Cellulose nanocrystals (CNCs) are promising bio-sourced building blocks for the production of high performance materials. In the last ten years, CNCs have been used in conjunction with polymers for the design of multilayered thin films via the layer-by-layer assembly technique. Herein, polymer chains have been replaced with positively charged inorganic gibbsite nanoplatelets (GN) to form hybrid “nanoparticle-only” composite films. A combination of atomic force microscopy and neutron reflectivity experiments was exploited to investigate the growth and structure of the films. Data show that the growth and density of GN/CNC films can be tuned over a wide range during preparation by varying the ionic strength in the CNC suspension and the film drying protocol. Specifically, thin and dense multilayered films or very thick, more porous mixed slabs, as well as intermediate internal structures could be obtained in a predictable manner. The influence of key physicochemical parameters on the multilayer film build up was elucidated and the film architecture was linked to the dominating interaction forces between components. The degree of structural control over these hybrid nanoparticle-only films is much higher than that reported for CNC/polymer films, which offers new properties and potential applications as separation membranes or flame retardant coatings

A preliminary overview of the multiconjugate adaptive optics module for the E-ELT

ABSTRACT The multi-conjugate adaptive optics module for the European Extremely Large Telescope has to provide a corrected field of medium to large size (up to 2 arcmin), over the baseline wavelength range 0.8-2.4 µm. The current design is characterized by two post-focal deformable mirrors, that complement the correction provided by the adaptive telescope; the wavefront sensing is performed by means of a high-order multiple laser guide star wavefront sensor and by a loworder natural guide star wavefront sensor. The present status of a two years study for the advanced conceptual design of this module is reported

The Genome of Rhyzopertha dominica (Fab.) (Coleoptera: Bostrichidae): Adaptation for Success

The lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), is a major global pest of cereal grains. Infestations are difficult to control as larvae feed inside grain kernels, and many populations are resistant to both contact insecticides and fumigants. We sequenced the genome of R. dominica to identify genes responsible for important biological functions and develop more targeted and efficacious management strategies. The genome was assembled from long read sequencing and long-range scaffolding technologies. The genome assembly is 479.1 Mb, close to the predicted genome size of 480.4 Mb by flow cytometry. This assembly is among the most contiguous beetle assemblies published to date, with 139 scaffolds, an N50 of 53.6 Mb, and L50 of 4, indicating chromosome-scale scaffolds. Predicted genes from biologically relevant groups were manually annotated using transcriptome data from adults and different larval tissues to guide annotation. The expansion of carbohydrase and serine peptidase genes suggest that they combine to enable efficient digestion of cereal proteins. A reduction in the copy number of several detoxification gene families relative to other coleopterans may reflect the low selective pressure on these genes in an insect that spends most of its life feeding internally. Chemoreceptor genes contain elevated numbers of pseudogenes for odorant receptors that also may be related to the recent ontogenetic shift of R. dominica to a diet consisting primarily of stored grains. Analysis of repetitive sequences will further define the evolution of bostrichid beetles compared to other species. The data overall contribute significantly to coleopteran genetic research

Impact du bruit de phase sur le transfert de fréquences avec des liens optiques sol-satellite asymetriques aller-retour utilisant la détection cohérente

International audienceBidirectional ground-satellite laser links suffer from turbulence-induced scintillation and phase distortion. We study how turbulence impacts on coherent detection capacity and on the associated phase noise that restricts clock transfer precision. We evaluate the capacity to obtain a two-way cancellation of atmospheric effects despite the asymmetry between up and down link that limits the link reciprocity. For ground-satellite links, the asymmetry is induced by point-ahead angle and possibly the use, for the ground terminal, of different transceiver diameters, in reception and emission. The quantitative analysis is obtained thanks to refined end- to-end simulations under realistic turbulence and wind conditions as well as satellite cinematic. These temporally resolved simulations allow characterizing the coherent detection in terms of time series of heterodyne efficiency for different system parameters. We show that Tip/Tilt correction on ground is mandatory at reception for the down link and as a pre-compensation of the up link. Good correlation between up and down phase noise is obtained even with asymmetric apertures of the ground transceiver and in spite of pointing ahead angle. The reduction to less than 1 rad2 of the two-way differential phase noise is very promising for clock comparisons.Les liens sol-satellite bidirectionnels par laser sont impactés par des effets de scintillation et de distorsion de phase, causés par la turbulence atmosphérique. Nous étudions comment la turbulence impacte la performance de la détection cohérente et celle du bruit de phase qui réduit la précision du transfert des horloges. Nous évaluons la capacité à obtenir une annulation des effets atmosphériques en dépit de l’asymétrie entre le lien montant et descendant limitant la réciprocité du lien. Pour les liens sol-satellite, l’asymétrie provient du pointage en avant et de l’utilisation possible pour le terminal sol, de différents diamètres pour l’émetteur et le récepteur. L’analyse quantitative est faite grâce à des simulations fines et bout en bout sous des conditions de turbulence et de vent réalistes, en tenant compte de la cinématique du satellite. Les simulations utilisent le principe de réciprocité pour estimer les performances du lien descendant et montant à partir de la propagation de 2 ondes planes descendantes. Ces simulations résolues temporellement permettent de caractériser la détection cohérente en termes de séries temporelles du rendement hétérodyne pour différents paramètres système. Nous montrons que la correction de Tip/Tilt est nécessaire à la réception du lien descendant et pour pré-compenser le lien montant. Une bonne corrélation entre les bruits de phase montant et descendant est obtenue même avec des ouvertures différentes de l’émetteur récepteur au sol et malgré le pointage en avant. La réduction à moins de 1 rad² du bruit de phase différentiel aller-retour est très prometteuse pour le transfert des horloges

Turbulent phase noise on asymmetric two-way ground-satellite coherent optical links

International audienceBidirectional ground-satellite laser links suffer from turbulence-induced scintillation and phase distortion. We study how turbulence impacts on coherent detection capacity and on the associated phase noise that restricts clock transfer precision. We evaluate the capacity to obtain a two-way cancellation of atmospheric effects despite the asymmetry between up and down link that limits the link reciprocity. For ground-satellite links, the asymmetry is induced by point-ahead angle and possibly the use, for the ground terminal, of different transceiver diameters, in reception and emission. The quantitative analysis is obtained thanks to refined end-to-end simulations under realistic turbulence and wind conditions as well as satellite cinematic. Simulations make use of the reciprocity principle to estimate both down and up link performance from wave-optics propagation of descending plane waves. These temporally resolved simulations allow characterising the coherent detection in terms of time series of heterodyne efficiency for different system parameters. We show Tip/Tilt correction on ground is mandatory at reception for the down link and as a pre-compensation of the up link. Good correlation between up and down phase noise is obtained even with asymmetric apertures of the ground transceiver and in spite of pointing ahead angle. The reduction to less than 1 rad<SUP>2</SUP> of the two-way differential phase noise is very promising for clock transfer

Impact of turbulence on high-precision ground-satellite frequency transfer with two-way coherent optical links

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Interest of old trees for saproxylic beetles across closing degree of background in Mediterranean landscapes

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Differential focal anisoplanatism in laser guide star wavefront sensing on extremely large telescopes

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