794 research outputs found
The effect of rotation and tidal heating on the thermal lightcurves of Super Mercuries
Short period (<50 days) low-mass (<10Mearth) exoplanets are abundant and the
few of them whose radius and mass have been measured already reveal a diversity
in composition. Some of these exoplanets are found on eccentric orbits and are
subjected to strong tides affecting their rotation and resulting in significant
tidal heating. Within this population, some planets are likely to be depleted
in volatiles and have no atmosphere. We model the thermal emission of these
"Super Mercuries" to study the signatures of rotation and tidal dissipation on
their infrared light curve. We compute the time-dependent temperature map at
the surface and in the subsurface of the planet and the resulting
disk-integrated emission spectrum received by a distant observer for any
observation geometry. We calculate the illumination of the planetary surface
for any Keplerian orbit and rotation. We include the internal tidal heat flow,
vertical heat diffusion in the subsurface and generate synthetic light curves.
We show that the different rotation periods predicted by tidal models
(spin-orbit resonances, pseudo-synchronization) produce different photometric
signatures, which are observable provided that the thermal inertia of the
surface is high, like that of solid or melted rocks (but not regolith). Tidal
dissipation can also directly affect the light curves and make the inference of
the rotation more difficult or easier depending on the existence of hot spots
on the surface. Infrared light curve measurement with the James Webb Space
Telescope and EChO can be used to infer exoplanets' rotation periods and
dissipation rates and thus to test tidal models. This data will also constrain
the nature of the (sub)surface by constraining the thermal inertia.Comment: 15 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Control of Transport-barrier relaxations by Resonant Magnetic Perturbations
Transport-barrier relaxation oscillations in the presence of resonant
magnetic perturbations are investigated using three-dimensional global fluid
turbulence simulations from first principles at the edge of a tokamak. It is
shown that resonant magnetic perturbations have a stabilizing effect on these
relaxation oscillations and that this effect is due mainly to a modification of
the pressure profile linked to the presence of both residual residual magnetic
island chains and a stochastic layer.Comment: 4 page
Effect of time-varying flow-shear on the nonlinear stability of the boundary of magnetized toroidal plasmas
We propose a phenomenological yet general model in a form of extended complex Ginzburg-Landau equation to understand edge-localized modes (ELMs), a class of quasi-periodic fluid instabilities in the boundary of toroidal magnetized high-temperature plasmas. The model reproduces key dynamical features of the ELMs (except the final explosive relaxation stage) observed in the high-confinement state plasmas on the Korea Superconducting Tokamak Advanced Research: quasi-steady states characterized by field-aligned filamentary eigenmodes, transitions between different quasi-steady eigenmodes, and rapid transition to non-modal filamentary structure prior to the relaxation. It is found that the inclusion of time-varying perpendicular sheared flow is crucial for reproducing all of the observed dynamical features
Pattern of Reaction Diffusion Front in Laminar Flows
Autocatalytic reaction between reacted and unreacted species may propagate as
solitary waves, namely at a constant front velocity and with a stationary
concentration profile, resulting from a balance between molecular diffusion and
chemical reaction. The effect of advective flow on the autocatalytic reaction
between iodate and arsenous acid in cylindrical tubes and Hele-Shaw cells is
analyzed experimentally and numerically using lattice BGK simulations. We do
observe the existence of solitary waves with concentration profiles exhibiting
a cusp and we delineate the eikonal and mixing regimes recently predicted.Comment: 4 pages, 3 figures. This paper report on experiments and simulations
in different geometries which test the theory of Boyd Edwards on flow
advection of chemical reaction front which just appears in PRL (PRL Vol
89,104501, sept2002
Emotional expressiveness of 5–6 month-old infants born very premature versus full-term at initial exposure to weaning foods
Facial expressions of 5–6 month-old infants born preterm and at term were compared while tasting for the first time solid foods (two fruit and two vegetable purées) given by the mother. Videotapes of facial reactions to these foods were objectively coded during the first six successive spoons of each test food using Baby FACS and subjectively rated by naïve judges. Infant temperament was also assessed by the parents using the Infant Behaviour Questionnaire. Contrary to our expectations, infants born preterm expressed fewer negative emotions than infants born full-term. Naïve judges rated infants born preterm as displaying more liking than their full-term counterparts when tasting the novel foods. The analysis of facial expressions during the six spoonfuls of four successive meals (at 1-week intervals) suggested a familiarization effect with the frequency of negative expressions decreasing after tasting the second spoon, regardless of infant age, type of food and order of presentation. Finally, positive and negative dimensions of temperament reported by the parents were related with objective and subjective coding of affective reactions toward foods in infants born preterm or full-term. Our research indicates that premature infants are more accepting of novel foods than term infants and this could be used for supporting the development of healthy eating patterns in premature infants. Further research is needed to clarify whether reduced negativity by infants born prematurely to the exposure to novel solid foods reflects a reduction of an adaptive avoidant behaviour during the introduction of novel foods
Le matériau sol-chaux comme une matériau résistant à l'érosion pour les ouvrages hydrauliques : état de l'art et projet de R&D français DigueElite
International audienceThe treatment of silty and clayey soils with lime (calcium oxide or hydroxide) is a technique widely used for soils improvement and stabilization for construction of roads, highways, railways, platforms. However, the principles of lime treatment for hydraulic earthen structures remains barely applied or even forgotten (European case). If existing testimonials (levees, dams, mainly in US and Australia) are evidences that show effectiveness and durability of lime-treated structures, there was a necessity to evaluate a series of unknown characteristics and relevant properties of lime-treated soils for an application in hydraulic context, through laboratory studies and full-scale experiments
Effect of the stellar spin history on the tidal evolution of close-in planets
We investigate how the evolution of the stellar spin rate affects, and is
affected by, planets in close orbits, via star-planet tidal interactions. To do
this, we used a standard equilibrium tidal model to compute the orbital
evolution of single planets orbiting both Sun-like stars and 0.1 M\odot
M-dwarfs. We tested two stellar spin evolution profiles, one with fast initial
rotation (P=1.2 day) and one with slow initial rotation (P=8 day). We tested
the effect of varying the stellar and planetary dissipation and the planet's
mass and initial orbital radius. Conclusions: Tidal evolution allows to
differentiate the early behaviors of extremely close-in planets orbiting either
a rapidly rotating star or a slowly rotating star. The early spin-up of the
star allows the close-in planets around fast rotators to survive the early
evolution. For planets around M-dwarfs, surviving the early evolution means
surviving on Gyr timescales whereas for Sun-like stars the spin-down brings
about late mergers of Jupiter planets. In light of this study, we can say that
differentiating between one spin evolution from another given the present
position of planets can be very tricky. Unless we can observe some markers of
former evolution it is nearly impossible to distinguish the two very different
spin profiles, let alone intermediate spin profiles. Though some conclusions
can still be drawn from statistical distributions of planets around fully
convective M-dwarfs. However, if the tidal evolution brings about a merger late
in its history it can also entail a noticeable acceleration of the star in late
ages, so that it is possible to have old stars that spin rapidly. This raises
the question of better constraining the age of stars
Increased insolation threshold for runaway greenhouse processes on Earth like planets
Because the solar luminosity increases over geological timescales, Earth
climate is expected to warm, increasing water evaporation which, in turn,
enhances the atmospheric greenhouse effect. Above a certain critical
insolation, this destabilizing greenhouse feedback can "runaway" until all the
oceans are evaporated. Through increases in stratospheric humidity, warming may
also cause oceans to escape to space before the runaway greenhouse occurs. The
critical insolation thresholds for these processes, however, remain uncertain
because they have so far been evaluated with unidimensional models that cannot
account for the dynamical and cloud feedback effects that are key stabilizing
features of Earth's climate. Here we use a 3D global climate model to show that
the threshold for the runaway greenhouse is about 375 W/m, significantly
higher than previously thought. Our model is specifically developed to quantify
the climate response of Earth-like planets to increased insolation in hot and
extremely moist atmospheres. In contrast with previous studies, we find that
clouds have a destabilizing feedback on the long term warming. However,
subsident, unsaturated regions created by the Hadley circulation have a
stabilizing effect that is strong enough to defer the runaway greenhouse limit
to higher insolation than inferred from 1D models. Furthermore, because of
wavelength-dependent radiative effects, the stratosphere remains cold and dry
enough to hamper atmospheric water escape, even at large fluxes. This has
strong implications for Venus early water history and extends the size of the
habitable zone around other stars.Comment: Published in Nature. Online publication date: December 12, 2013.
Accepted version before journal editing and with Supplementary Informatio
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