Possible climates on terrestrial exoplanets

What kind of environment may exist on terrestrial planets around other stars? In spite of the lack of direct observations, it may not be premature to speculate on exoplanetary climates, for instance to optimize future telescopic observations, or to assess the probability of habitable worlds. To first order, climate primarily depends on 1) The atmospheric composition and the volatile inventory; 2) The incident stellar flux; 3) The tidal evolution of the planetary spin, which can notably lock a planet with a permanent night side. The atmospheric composition and mass depends on complex processes which are difficult to model: origins of volatile, atmospheric escape, geochemistry, photochemistry. We discuss physical constraints which can help us to speculate on the possible type of atmosphere, depending on the planet size, its final distance for its star and the star type. Assuming that the atmosphere is known, the possible climates can be explored using Global Climate Models analogous to the ones developed to simulate the Earth as well as the other telluric atmospheres in the solar system. Our experience with Mars, Titan and Venus suggests that realistic climate simulators can be developed by combining components like a "dynamical core", a radiative transfer solver, a parametrisation of subgrid-scale turbulence and convection, a thermal ground model, and a volatile phase change code. On this basis, we can aspire to build reliable climate predictors for exoplanets. However, whatever the accuracy of the models, predicting the actual climate regime on a specific planet will remain challenging because climate systems are affected by strong positive destabilizing feedbacks (such as runaway glaciations and runaway greenhouse effect). They can drive planets with very similar forcing and volatile inventory to completely different states.Comment: In press, Proceedings of the Royal Society A 31 pages, 6 figure

Comment on " Gain coefficient method for amplified spontaneous emission in thin waveguided film of a conjugated polymer " [APL 93, 163307 (2008)]

Comment on " Gain coefficient method for amplified spontaneous emission in thin waveguided film of a conjugated polymer " [APL 93, 163307 (2008)

Longitudinal magnetoresistance in Co-doped BaFe2As2 and LiFeAs single crystals: Interplay between spin fluctuations and charge transport in iron-pnictides

The longitudinal in-plane magnetoresistance (LMR) has been measured in different Ba(Fe_(1-x)Co_x)2As2 single crystals and in LiFeAs. For all these compounds, we find a negative LMR in the paramagnetic phase whose magnitude increases as H^2. We show that this negative LMR can be readily explained in terms of suppression of the spin fluctuations by the magnetic field. In the Co-doped samples, the absolute value of the LMR coefficient is found to decrease with doping content in the paramagnetic phase. The analysis of its T dependence in an itinerant nearly antiferromagnetic Fermi liquid model evidences that the LMR displays a qualitative change of T variation with increasing Co content. The latter occurs at optimal doping for which the antiferromagnetic ground state is suppressed. The same type of analysis for the negative LMR measured in LiFeAs suggests that this compound is on the verge of magnetism.Comment: 6 pages, 6 figure

Seven-year climatology of dust opacity on Mars

This paper describes the procedure we have used to produce multi-annual dust scenarios for Martian years 24 to 30 from a multi-instrument dataset of total dust opacity observations. This procedure includes gridding the observations on a pre-defined longitude-latitude grid with 1 sol resolution in time, and spatially interpolating the results to obtain complete daily maps of total dust opacity. We used weighted binning as gridding technique, and spatial kriging as method of interpolation. The new dust scenarios are available as NetCDF files, easy to interface to any model including global circulation and mesoscale models for the Martian atmosphere

High Field determination of superconducting fluctuations in high-Tc cuprates

Large pulsed magnetic fields up to 60 Tesla are used to suppress the contribution of superconducting fluctuations (SCF) to the ab-plane conductivity above Tc in a series of YBa2Cu3O6+x single crystals. The fluctuation conductivity is found to vanish nearly exponentially with temperature, allowing us to determine precisely the field H'c(T) and the temperature T'c above which the SCFs are fully suppressed. T'c is always found much smaller than the pseudogap temperature. A careful investigation near optimal doping shows that T'c is higher than the pseudogap T*, which indicates that the pseudogap cannot be assigned to preformed pairs. For nearly optimally doped samples, the fluctuation conductivity can be accounted for by gaussian fluctuations following the Ginzburg-Landau scheme. A phase fluctuation contribution might be invoked for the most underdoped samples in a T range which increases when controlled disorder is introduced by electron irradiation. Quantitative analysis of the fluctuating magnetoconductance allows us to determine the critical field Hc2(0) which is found to be quite similar to H'c(0) and to increase with hole doping. Studies of the incidence of disorder on both T'c and T* enable us to propose a three dimensional phase diagram including a disorder axis, which allows to explain most observations done in other cuprate families.Comment: 10 pages, 10 figures, invited paper at the M2SHTSC Conference Washington (2012

Rencontre avec un nomade moderne : Le full-time RVer

L’appel de la route, si présent ces dernières décennies en Amérique du Nord, connaît un regain de popularité auprès des full-time RVers (caravaniers à plein temps). Ces personnes décident de tout quitter pour vivre uniquement dans leur véhicule récréatif et sillonner les routes nord-américaines. Ils sont les nouveaux nomades de l’Amérique du Nord. Leur mode de vie est basé sur une mobilité permanente, délibérée, s’effectuant sur le continent américain, ce qui ne génère ainsi qu’un faible fossé culturel et qui les différencie des autres groupes migrants et nomades. Cette population, peu connue des recherches scientifiques, concerne pourtant plusieurs millions de Nord-américains. Cet article propose de faire connaissance avec ces nomades modernes, de savoir qui ils sont, où ils vivent et de comprendre leurs stratégies d’adaptation envers des concepts aussi fondamentaux que celui de la famille.The call of the open road, so strongly felt over the last decades in North America, has experienced renewed popularity among full-time RVers. These individuals decide to leave everything behind in order to live only in their recreational vehicles and to crisscross the roadways of North America. They are the new nomads of North America. Their lifestyle is based on deliberate permanent mobility with the entire North American continent as their home base — thus generating only the slightest cultural gap — a chosen mobility which also distinguishes them from other groups of migrants and nomads. This population group has been the subject of very little scientific research yet millions of North Americans belong to its ranks. This article intends to introduce these modern-day nomads, providing information as to who they are and where they live and elucidating their strategies of adaptation with respect to such fundamental concepts as that of the family