431 research outputs found
Cross-Layer Early Reliability Evaluation for the Computing cOntinuum
Advanced multifunctional computing systems realized in forthcoming technologies hold the promise of a significant increase of the computational capability that will offer end-users ever improving services and functionalities (e.g., next generation mobile devices, cloud services, etc.). However, the same path that is leading technologies toward these remarkable achievements is also making electronic devices increasingly unreliable, posing a threat to our society that is depending on the ICT in every aspect of human activities. Reliability of electronic systems is therefore a key challenge for the whole ICT technology and must be guaranteed without penalizing or slowing down the characteristics of the final products. CLERECO EU FP7 (GA No. 611404) research project addresses early accurate reliability evaluation and efficient exploitation of reliability at different design phases, since these aspects are two of the most important and challenging tasks toward this goal
Advances in the Engineering of Near Infrared Emitting Liquid Crystals and Copolymers, Extended Porous Frameworks, Theranostic Tools and Molecular Junctions Using Tailored Re6 Cluster Building Blocks
International audienceAt the occasion of the fiftieth birthday of the introduction of the term 'metal atom cluster' by F. A. Cotton in inorganic chemistry, it is the good time to make a review on the advances in the engineering of molecular assemblies and nanomaterials based on octahedral Re6 metal atom clusters. The latter exhibit unique intrinsic structural and physicochemical properties (orthogonal disposition of metallic sites that can be selectively functionalized, photoluminescence, redox, generation of singlet oxygen) that make them relevant building blocks for the structuration at the nanometric scale and functionalization of hybrid organic-inorganic materials and supramolecular frameworks. After synthesis by solid state chemistry techniques at high temperature, inorganic precursors built up on face-capped [(Re6Yi8)Ya6] cluster units (Y = chalcogen and/or halogen) can be functionalized via solution chemistry techniques or organic melts to form [(Re6Yi8)La6] (L = CN, OH, various organic ligands...). This work reports advances in the synthesis of [(Re6Yi8)Ya6] and [(Re6Yi8)La6] cluster units as well as on their use in the elaboration of supramolecular frameworks, nanoparticles, hybrid nanomaterials (co-polymers and liquid crystals) and active molecular junctions
Mass-radius relationships for exoplanets
For planets other than Earth, interpretation of the composition and structure
depends largely on comparing the mass and radius with the composition expected
given their distance from the parent star. The composition implies a
mass-radius relation which relies heavily on equations of state calculated from
electronic structure theory and measured experimentally on Earth. We lay out a
method for deriving and testing equations of state, and deduce mass-radius and
mass-pressure relations for key materials whose equation of state is reasonably
well established, and for differentiated Fe/rock. We find that variations in
the equation of state, such as may arise when extrapolating from low pressure
data, can have significant effects on predicted mass- radius relations, and on
planetary pressure profiles. The relations are compared with the observed
masses and radii of planets and exoplanets. Kepler-10b is apparently 'Earth-
like,' likely with a proportionately larger core than Earth's, nominally 2/3 of
the mass of the planet. CoRoT-7b is consistent with a rocky mantle over an
Fe-based core which is likely to be proportionately smaller than Earth's. GJ
1214b lies between the mass-radius curves for H2O and CH4, suggesting an 'icy'
composition with a relatively large core or a relatively large proportion of
H2O. CoRoT-2b is less dense than the hydrogen relation, which could be
explained by an anomalously high degree of heating or by higher than assumed
atmospheric opacity. HAT-P-2b is slightly denser than the mass-radius relation
for hydrogen, suggesting the presence of a significant amount of matter of
higher atomic number. CoRoT-3b lies close to the hydrogen relation. The
pressure at the center of Kepler-10b is 1.5+1.2-1.0 TPa. The central pressure
in CoRoT-7b is probably close to 0.8TPa, though may be up to 2TPa.Comment: Added more recent exoplanets. Tidied text and references. Added extra
"rock" compositions. Responded to referee comment
Invariant Representative Cocycles of Cohomology Generators using Irregular Graph Pyramids
Structural pattern recognition describes and classifies data based on the
relationships of features and parts. Topological invariants, like the Euler
number, characterize the structure of objects of any dimension. Cohomology can
provide more refined algebraic invariants to a topological space than does
homology. It assigns `quantities' to the chains used in homology to
characterize holes of any dimension. Graph pyramids can be used to describe
subdivisions of the same object at multiple levels of detail. This paper
presents cohomology in the context of structural pattern recognition and
introduces an algorithm to efficiently compute representative cocycles (the
basic elements of cohomology) in 2D using a graph pyramid. An extension to
obtain scanning and rotation invariant cocycles is given.Comment: Special issue on Graph-Based Representations in Computer Visio
DNA Nucleobase Synthesis at Titan Atmosphere Analog by Soft X-rays
Titan, the largest satellite of Saturn, has an atmosphere chiefly made up of
N2 and CH4 and includes traces of many simple organic compounds. This
atmosphere also partly consists of haze and aerosol particles which during the
last 4.5 gigayears have been processed by electric discharges, ions, and
ionizing photons, being slowly deposited over the Titan surface. In this work,
we investigate the possible effects produced by soft X-rays (and secondary
electrons) on Titan aerosol analogs in an attempt to simulate some prebiotic
photochemistry. The experiments have been performed inside a high vacuum
chamber coupled to the soft X-ray spectroscopy beamline at the Brazilian
Synchrotron Light Source, Campinas, Brazil. In-situ sample analyses were
performed by a Fourier transform infrared spectrometer. The infrared spectra
have presented several organic molecules, including nitriles and aromatic CN
compounds. After the irradiation, the brownish-orange organic residue (tholin)
was analyzed ex-situ by gas chromatographic (GC/MS) and nuclear magnetic
resonance (1H NMR) techniques, revealing the presence of adenine (C5H5N5), one
of the constituents of the DNA molecule. This confirms previous results which
showed that the organic chemistry on the Titan surface can be very complex and
extremely rich in prebiotic compounds. Molecules like these on the early Earth
have found a place to allow life (as we know) to flourish.Comment: To appear in Journal of Physical Chemistry A.; Number of pages: 6;
Number of Figures: 5; Number of Tables: 1; Number of references:49; Full
paper at http://pubs.acs.org/doi/abs/10.1021/jp902824
Equation of state and phonon frequency calculations of diamond at high pressures
The pressure-volume relationship and the zone-center optical phonon frequency
of cubic diamond at pressures up to 600 GPa have been calculated based on
Density Functional Theory within the Local Density Approximation and the
Generalized Gradient Approximation. Three different approaches, viz. a
pseudopotential method applied in the basis of plane waves, an all-electron
method relying on Augmented Plane Waves plus Local Orbitals, and an
intermediate approach implemented in the basis of Projector Augmented Waves
have been used. All these methods and approximations yield consistent results
for the pressure derivative of the bulk modulus and the volume dependence of
the mode Grueneisen parameter of diamond. The results are at variance with
recent precise measurements up to 140 GPa. Possible implications for the
experimental pressure determination based on the ruby luminescence method are
discussed.Comment: 10 pages, 6 figure
Transiting exoplanets from the CoRoT space mission VIII. CoRoT-7b: the first Super-Earth with measured radius
We report the discovery of very shallow (DF/F = 3.4 10-4), periodic dips in
the light curve of an active V = 11.7 G9V star observed by the CoRoT satellite,
which we interpret as due to the presence of a transiting companion. We
describe the 3-colour CoRoT data and complementary ground-based observations
that support the planetary nature of the companion. Methods. We use CoRoT color
information, good angular resolution ground-based photometric observations in-
and out- of transit, adaptive optics imaging, near-infrared spectroscopy and
preliminary results from Radial Velocity measurements, to test the diluted
eclipsing binary scenarios. The parameters of the host star are derived from
optical spectra, which were then combined with the CoRoT light curve to derive
parameters of the companion. We examine carefully all conceivable cases of
false positives, and all tests performed support the planetary hypothesis.
Blends with separation larger than 0.40 arcsec or triple systems are almost
excluded with a 8 10-4 risk left. We conclude that, as far as we have been
exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which
we derive a period of 0.853 59 +/- 3 10-5 day and a radius of Rp = 1.68 +/-
0.09 REarth. Analysis of preliminary radial velocity data yields an upper limit
of 21 MEarth for the companion mass, supporting the finding.
CoRoT-7b is very likely the first Super-Earth with a measured radius.Comment: Accepted in Astronomy and Astrophysics; typos and language
corrections; version sent to the printer w few upgrade
The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert
To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets’ mass and radius with a good precision (≲10%) is essential. To achieve this purpose the discovery of transiting exoplanets around bright stars is of prime interest. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15%. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31−0.03+0.04 MJ, 1.13−0.03+0.03 RJ, 0.22−0.02+0.03 ρJ and 1290−10+20 K, and 0.39−0.02+0.02 MJ, 1.55−0.08+0.10 RJ, 0.11−0.02+0.02 ρJ and 1700−40+40 K, respectively. Their host stars are early G type stars (with mag V ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a super-Neptune orbiting a K type star (mag V = 11.6). It has a mass of 0.128−0.009+0.010 MJ, a radius of 0.51−0.02+0.02 RJ, a density of 1.0−0.1+0.1 ρJ, an equilibrium temperature of 970−20+30 K and an orbital period of 3.83 days. The radius of WASP-151b appears to be only slightly inflated, while WASP-153b presents a significant radius anomaly compared to a recently published model. WASP-156b, being one of the few well characterized super-Neptunes, will help to constrain the still debated formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms an already observed tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behavior for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population
Characterising the Atmospheres of Transiting Planets with a Dedicated Space Telescope
Exoplanetary science is one of the fastest evolving fields of today's astronomical research, continuously yielding unexpected and surprising results. Ground-based planet-hunting surveys, together with dedicated space missions such as Kepler and CoRoT, are delivering an ever-increasing number of exoplanets, over 690, and ESA's Gaia mission will escalate the exoplanetary census into the several thousands. The next logical step is the characterization of these new worlds. What is their nature? Why are they as they are? Use of the Hubble Space Telescope and Spitzer Space Telescope to probe the atmospheres of transiting hot, gaseous exoplanets has opened perspectives unimaginable even just 10 years ago, demonstrating that it is indeed possible with current technology to address the ambitious goal of characterizing the atmospheres of these alien worlds. However, these successful measurements have also shown the difficulty of understanding the physics and chemistry of these exotic environments when having to rely on a limited number of observations performed on a handful of objects. To progress substantially in this field, a dedicated facility for exoplanet characterization, able to observe a statistically significant number of planets over time and a broad spectral range will be essential. Additionally, the instrument design (e.g., detector performances, photometric stability) will be tailored to optimize the extraction of the astrophysical signal. In this paper, we analyze the performance and tradeoffs of a 1.2/1.4 m space telescope for exoplanet transit spectroscopy from the visible to the mid-IR. We present the signal-to-noise ratio as a function of integration time and stellar magnitude/spectral type for the acquisition of spectra of planetary atmospheres for a variety of scenarios: hot, warm, and temperate planets orbiting stars ranging in spectral type from hot F- to cooler M-dwarfs. Our results include key examples of known planets (e.g., HD 189733b, GJ 436b, GJ 1214b, and Cancri 55 e) and simulations of plausible terrestrial and gaseous planets, with a variety of thermodynamical conditions. We conclude that even most challenging targets, such as super-Earths in the habitable zone of late-type stars, are within reach of an M-class, space-based spectroscopy mission
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