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See detailSPHERE+: Imaging young Jupiters down to the snowline
Boccaletti, A.; Chauvin, G.; Mouillet, D. et al

E-print/Working paper (2020)

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating ... [more ▼]

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating modes, primarily in the field of direct imaging of exoplanetary systems, focusing on exoplanets as point sources and circumstellar disks as extended objects. The achievements obtained thus far with SPHERE (~200 refereed publications) in different areas (exoplanets, disks, solar system, stellar physics...) have motivated a large consortium to propose an even more ambitious set of science cases, and its corresponding technical implementation in the form of an upgrade. The SPHERE+ project capitalizes on the expertise and lessons learned from SPHERE to push high contrast imaging performance to its limits on the VLT 8m-telescope. The scientific program of SPHERE+ described in this document will open a new and compelling scientific window for the upcoming decade in strong synergy with ground-based facilities (VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and WFIRST). While SPHERE has sampled the outer parts of planetary systems beyond a few tens of AU, SPHERE+ will dig into the inner regions around stars to reveal and characterize by mean of spectroscopy the giant planet population down to the snow line. Building on SPHERE's scientific heritage and resounding success, SPHERE+ will be a dedicated survey instrument which will strengthen the leadership of ESO and the European community in the very competitive field of direct imaging of exoplanetary systems. With enhanced capabilities, it will enable an even broader diversity of science cases including the study of the solar system, the birth and death of stars and the exploration of the inner regions of active galactic nuclei. [less ▲]

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See detailTunable surface boundary conditions in strain gradient crystal plasticity model
Yuan, Sibo ULiege; Duchene, Laurent ULiege; Keller, C. et al

in Mechanics of Materials (2020), 145

The behavior of dislocations in the neighborhood of a metallurgical interface or a free surface can be totally different depending on the boundary conditions. Dislocations cease to move and accumulate ... [more ▼]

The behavior of dislocations in the neighborhood of a metallurgical interface or a free surface can be totally different depending on the boundary conditions. Dislocations cease to move and accumulate around impermeable interfaces, such as grain boundaries or hard (i.e. coated or oxidized) external surfaces. On the contrary, dislocations annihilate on free surfaces, as supported by the image force concept. However the behavior of dislocations depends on the true surface permeability, which falls between these two idealized cases. In this paper, two different numerical methods are applied to model the intermediate surface behaviors: the virtual image geometrically necessary dislocation approach and the generalized elastic foundation approach while a strain gradient crystal plasticity constitutive law simulates the response of a Ni single crystal. It is demonstrated that a uniform dislocation density field on the surface can only be obtained by a variant of the generalized elastic foundation approach. © 2020 Elsevier Ltd [less ▲]

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See detailReview of high-contrast imaging systems for current and future ground- and space-based telescopes I: coronagraph design methods and optical performance metrics
Ruane, G.; Riggs, A.; Mazoyer, J. et al

in Lystrup, M.; MacEwen, H.; Fazio, G. (Eds.) et al Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave (2018, August 21)

The Optimal Optical Coronagraph (OOC) Workshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 25 researchers working on exoplanet instrumentation to ... [more ▼]

The Optimal Optical Coronagraph (OOC) Workshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 25 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. In this first installment of a series of three papers summarizing the outcomes of the OOC workshop, we present an overview of design methods and optical performance metrics developed for coronagraph instruments. The design and optimization of coronagraphs for future telescopes has progressed rapidly over the past several years in the context of space mission studies for Exo-C, WFIRST, HabEx, and LUVOIR as well as ground-based telescopes. Design tools have been developed at several institutions to optimize a variety of coronagraph mask types. We aim to give a broad overview of the approaches used, examples of their utility, and provide the optimization tools to the community. Though it is clear that the basic function of coronagraphs is to suppress starlight while maintaining light from off-axis sources, our community lacks a general set of standard performance metrics that apply to both detecting and characterizing exoplanets. The attendees of the OOC workshop agreed that it would benefit our community to clearly define quantities for comparing the performance of coronagraph designs and systems. Therefore, we also present a set of metrics that may be applied to theoretical designs, testbeds, and deployed instruments. We show how these quantities may be used to easily relate the basic properties of the optical instrument to the detection significance of the given point source in the presence of realistic noise. [less ▲]

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See detailAtmospheric implications of light alkane emissions from the U.S. oil and gas sector
Fischer, Emily V; Tzompa Sosa, Zitely; Henderson, B et al

Conference (2017, December 14)

New efficient drilling techniques triggered a massive growth of unconventional oil and natural gas production in North America starting in 2005. Emissions of a variety of volatile organic compounds (VOCs ... [more ▼]

New efficient drilling techniques triggered a massive growth of unconventional oil and natural gas production in North America starting in 2005. Emissions of a variety of volatile organic compounds (VOCs) from the oil and gas sector occur during well development and production phases, and emissions to the atmosphere also continue when wells are abandoned. Determining VOC emission fluxes in the context of rapid growth of the oil and natural gas industry presents a big challenge for emission inventories. In the U.S., the latest version of the 2011 National Emission Inventory (NEI2011v6.3) includes updates over important oil and natural gas basins and speciation profiles based on the Western Regional Air Partnership. We incorporated the NEI2011v6.3 into the GEOS-Chem chemical transport model to simulate the atmospheric abundances of C2-C5 alkanes over the U.S. attributed to emissions from the oil and gas sector. We present results from a nested high-resolution (0.5 degree x 0.667 degree) simulation over North America. C2-C5 alkane emissions from NEI 2011v6.3 increase across the U.S. compared to the previous NEI 2011 v2 incorporated as default in GEOS-Chem. Ethane (C2H6) and propane (C3H8) emission fluxes increased over important oil and natural gas basins. We compare our simulation to a suite of surface observations, column measurements, and aircraft profiles. Finally, we estimate the contribution that C2-C5 alkanes make to the abundance and production of important secondary species including ozone, peroxy acetyl nitrate, and several ketones. [less ▲]

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See detailSize effects and temperature dependence on strain-hardening mechanisms in some face centered cubic materials
HUG, E.; DUBOS, P.A.; keller, C. et al

in Mechanics of Materials (2015), 91

The mechanical behaviour of face centered cubic metals is deeply affected when specimen dimensions decrease from a few The millimeters to a few micrometers. At room temperature, a critical thickness (t ... [more ▼]

The mechanical behaviour of face centered cubic metals is deeply affected when specimen dimensions decrease from a few The millimeters to a few micrometers. At room temperature, a critical thickness (t) to grain size (d) ratio (t/d)c, was previously highlighted, under which the sofiening of mechanical properties became very pronounced both in terms of Hall-Petch relation and work hardening mechanisms. In this work, new experimental results are provided concerning the influence of temperature on this size effect for copper, nickel and Ni-20wt.%Cr, representative of a wide range of deformation mechanisms (i.e. dislocation slip character). It is shown that multicrystalline samples (t/d < (t/d)c) are not deeply affected by an increase in temperature, independently of the planar or wavy character of dislocation glide. For pronounced wavy slip character metals, surface effects in polycrystals (t/d > (t/d)c) are not significant enough to reduce the gap between polycrystal and multierystal mechanical behaviour when the temperature increases. However, a transition from wavy slip to planar glide mechanisms induces a modification ofthe polycrystalline behaviour which tends tovard multicrystalline one with a moderate increase in temperature. This work demonstrates that surface effects and grain size influence can be successfully disassociated for the three studied materials using an analysis supported by the Kooks- Mecking formalism. All these results are supported by microscopic investigations of dislocation substructures and compared to numerical simulations using a stress gradient plasticity model. [less ▲]

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See detailSPICES: spectro-polarimetric imaging and characterization of exoplanetary systems. From planetary disks to nearby Super Earths
Boccaletti, Anthony; Schneider, Jean; Traub, Wes et al

in Experimental Astronomy (2012), 34

SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period ... [more ▼]

SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450-900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5-10 AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses to Super Earths (̃2 Earth radii, ̃10 M[SUB]⊕[/SUB]) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System. [less ▲]

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