Mamadou N'Diaye

Red wine polyphenols induce EDHF-mediated relaxations in porcine coronary arteries through the redox-sensitive activation of the PI3-kinase/Akt pathway.

Red wine polyphenolic compounds (RWPCs) are potent inducers of endothelium‐dependent relaxations of coronary arteries, which involve both nitric oxide and endothelium‐derived hyperpolarizing factor (EDHF). The EDHF‐mediated relaxation to RWPCs is critically dependent on the formation of reactive oxygen species by a flavin‐dependent enzyme. The aim of the present study was to determine the role of redox‐sensitive protein kinases including p38 MAPK, ERK1/2 and PI3‐kinase/Akt in RWPCs‐induced EDHF‐mediated relaxation. Porcine coronary artery rings were suspended in organ chambers for measurement of changes in isometric tension. Confluent cultures of porcine coronary artery endothelial cells were used to determine the phosphorylation level of p38 MAPK, ERK1/2 and Akt by Western blot analysis. All experiments were performed in the presence of indomethacin and Nω‐nitro‐L‐arginine. RWPCs caused pronounced endothelium‐dependent relaxations, which were significantly reduced by wortmannin and LY294002, two inhibitors of PI3‐kinase, and not affected by PD98059 (an inhibitor of ERK1/2 kinase kinase) and SB203580 (an inhibitor of p38 MAPK). In contrast, wortmannin did not affect relaxations to bradykinin or levcromakalim. RWPCs elicited within minutes a sustained and concentration‐dependent phosphorylation of p38 MAPK, ERK1/2 and Akt in endothelial cells. The phosphorylation of Akt in response to RWPCs was abolished by wortmannin and LY294002, and by the membrane‐permeant analogue of superoxide dismutase Mn(III)tetrakis(1‐methyl‐4‐pyridyl)porphyrin. The present findings demonstrate that RWPCs cause EDHF‐mediated relaxations of coronary arteries; these responses are critically dependent on the redox‐sensitive activation of the PI3‐kinase/Akt pathway in endothelial cells.

Lab results of the circular phase mask concepts for high-contrast imaging of exoplanets

Circular phase mask concepts represent promising options for high contrast imaging and spectroscopy of exo-planets. Depending on their design, they can either work as a diffraction suppression system or as a focal plane wavefront sensor. While the apodized Roddier coronagraph uses a π-phase mask to obtain complete suppression of the star image in monochromatic light, the Zernike sensor uses a π/2-phase mask to measure the residual aberrations in the focal plane by encoding them into intensity variations in the relayed pupil. Implementations of the Zernike sensor can be considered in exoplanet imagers such as VLT-SPHERE, Gemini planet imager, Palomar-P1640 or Subaru-SCExAO to enlarge their capabilities. However, such concepts have not been validated experimentally up to now. Our goal is to perform lab demonstration of this concept on our visible coronagraph testbed at LAM and to propose an upgrade design for SPHERE. In this communication, we report on results of lab measurements of the Zernike sensor and determine its sensitivity to small wavefront errors.

Capabilities of ACAD-OSM, an active method for the correction of aperture discontinuities

The increasing complexity of the aperture geometry of the future space- and ground based-telescopes will limit the performance of the next generation of coronagraphic instruments for high contrast imaging of exoplanets. We propose here a new closed-loop optimization technique using two deformable mirrors to correct for the effects of complex apertures on coronagraph performance, alternative to the ACAD technique previously developed by our group. This technique, ACAD-OSM, allows the use of any coronagraphs designed for continuous apertures, with complex, segmented, apertures, maintaining high performance in contrast and throughput. We show the capabilities of this technique on several pupil geometries (segmented LUVOIR type aperture, WFIRST, ELTs) for which we obtained high contrast levels with several deformable mirror setups (size, number of actuators, separation between them), coronagraphs (apodized pupil Lyot and vortex coronagraphs) and spectral bandwidths, which will help us present recommendations for future coronagraphic instruments. We show that this active technique handles, without any revision to the algorithm, changing or unknown optical aberrations or discontinuities in the pupil, including optical design misalignments, missing segments and phase errors.

Tip/tilt optimizations for polynomial apodized vortex coronagraphs on obscured telescope pupils

Obstructions due to large secondary mirrors, primary mirror segmentation, and secondary mirror support struts all introduce diffraction artifacts that limit the performance offered by coronagraphs. However, just as vortex coronagraphs provides theoretically ideal cancellation of on-axis starlight for clear apertures, the Polynomial Apodized Vortex Coronagraph (PAVC) completely blocks on-axis light for apertures with central obscurations, and delivers off-axis throughput that improves as the topological charge of the vortex increases. We examine the sensitivity of PAVC designs to tip/tilt aberrations and stellar angular size, and discuss methods for mitigating these effects. By imposing additional constraints on the pupil plane apodization, we decrease the sensitivity of the PAVC to the small positional shifts of the on-axis source induced by either tip/tilt or stellar angular size; providing a route to overcoming an important hurdle facing the performance of vortex coronagraphs on telescopes with complicated pupils.

Experimental advances in phase mask coronagraphy

Stellar coronagraphy is a key technology for current and future instruments for exoplanet imaging and spectroscopy, both on the ground and in space. We pursue the research on coronagraphs based on circular phase masks and report in this paper on recent advances in terms of the trade between spectral bandwidth and achievable contrast. Circular phase masks combined with colored apodizations prove to be promising options in such coronagraphic systems to reach high contrast gains within the search area over a wide band of wavelengths.

Optimized High Order Explicit Runge-Kutta-Nyström Schemes

Runge-Kutta-Nystrom (RKN) schemes have been developed to solve a non-linear ordinary differential equation (ODE) of the type y″ = f(t, y). In Chawla and Sharma (Computing, 26:247–256, 1981), the stability condition (the Courant-Friedrichs-Lewy or CFL) associated with these schemes have been studied for order 3, 4 and 5. In this paper, we extend this study for higher orders and we propose a new algorithm to compute numerically the CFL. By using this algorithm, we compute optimal coefficients for RKN schemes of orders 6, 7, 8 and 10 which maximize the CFL. Herein, the obtained schemes are used to solve non-linear Maxwell’s equations in 1-D.