Collapse of massive magnetized dense cores using radiation-magneto-hydrodynamics: early fragmentation inhibition

We report the results of radiation-magneto-hydrodynamics calculations in the context of high mass star formation, using for the first time a self-consistent model for photon emission (i.e. via thermal emission and in radiative shocks) and with the high resolution necessary to resolve properly magnetic braking effects and radiative shocks on scales <100 AU. We investigate the combined effects of magnetic field, turbulence, and radiative transfer on the early phases of the collapse and the fragmentation of massive dense cores. We identify a new mechanism that inhibits initial fragmentation of massive dense cores, where magnetic field and radiative transfer interplay. We show that this interplay becomes stronger as the magnetic field strength increases. Magnetic braking is transporting angular momentum outwards and is lowering the rotational support and is thus increasing the infall velocity. This enhances the radiative feedback owing to the accretion shock on the first core. We speculate that highly magnetized massive dense cores are good candidates for isolated massive star formation, while moderately magnetized massive dense cores are more appropriate to form OB associations or small star clusters.Comment: Accepted for publication in ApJL, 19 pages, 4 figure

Dynamic Behaviour of a Flexible Yacht Sail Plan

• Dynamic fluid structure interaction of a sail plan is modeled in harmonic pitching • Aerodynamic forces oscillations show hysteresis phenomena • Neglecting the structural deformation underestimates the forces oscillations • Both aerodynamic and structure inertia affect loads in the rig.A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to address both issues of aerodynamic unsteadiness and structural deformation. The FSI model | Vortex Lattice Method uid model and Finite Element structure model | has been validated with full-scale measurements. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops, suggesting that some energy is exchanged by the system. The area included in the hysteresis loop increases with the motion reduced frequency and amplitude. Comparison of rigid versus soft structures shows that FSI increases the energy exchanged by the system and that the oscillations of aerodynamic forces are underestimated when the structure deformation is not considered. Dynamic loads in the fore and aft rigging wires are dominated by structural and inertial effects. This FSI model and the obtained results may be useful firstly for yacht design, and also in the field of auxiliary wind assisted ship propulsion, or to investigate other marine soft structures.This work was supported by the French Naval Academy

Surface Activity and Oscillation Amplitudes of Red Giants in Eclipsing Binaries

Among 19 red-giant stars belonging to eclipsing binary systems that have been identified in Kepler data, 15 display solar-like oscillations. We study whether the absence of mode detection in the remaining 4 is an observational bias or possibly evidence of mode damping that originates from tidal interactions. A careful analysis of the corresponding Kepler light curves shows that modes with amplitudes that are usually observed in red giants would have been detected if they were present. We observe that mode depletion is strongly associated with short-period systems, in which stellar radii account for 16-24 % of the semi-major axis, and where red-giant surface activity is detected. We suggest that when the rotational and orbital periods synchronize in close binaries, the red-giant component is spun up, so that a dynamo mechanism starts and generates a magnetic field, leading to observable stellar activity. Pressure modes would then be damped as acoustic waves dissipate in these fields.Comment: 11 pages, 10 figures, Accepted in Ap

Engel Curves, Spatial Variation in Prices and Demand for Commodities in Côte d'Ivoire

This paper aims to estimate the price and income elasticities of the demand for essential commodities in Cote d'Ivoire. Using data from the 2002 Cote d'Ivoire Living Standard Survey and a theoretical framework developed by Crawford et al. (2003), we analyse price effects on the demand for groups of commodities by exploiting a relationship between unit values and commodity quantities and deriving Engel curves. Our findings reveal that the own-price elasticity of meat and dairy products is considerably stronger for rich households (those in the 90th percentile of total expenditure) than for poor households (those in the 10th percentile of total expenditure). Although all the modelled groups of commodities are normal goods, the paper shows that starch is more of a necessity for poor households than for rich ones, whereas meat and dairy products are more of a luxury good for poor households than for rich households.consumer demand, unit values, developing country

Engel curves, spatial variation in prices and demand for commodities in Côte d'Ivoire

This paper aims to estimate the price and income elasticities of the demand for essential commodities in Cote d'Ivoire. Using data from the 2002 Cote d'Ivoire Living Standard Survey and a theoretical framework developed by Crawford et al. (2003), we analyse price effects on the demand for groups of commodities by exploiting a relationship between unit values and commodity quantities and deriving Engel curves. Our findings reveal that the own-price elasticity of meat and dairy products is considerably stronger for rich households (those in the 90th percentile of total expenditure) than for poor households (those in the 10th percentile of total expenditure). Although all the modelled groups of commodities are normal goods, the paper shows that starch is more of a necessity for poor households than for rich ones, whereas meat and dairy products are more of a luxury good for poor households than for rich households. --Consumer demand,Unit values,Developing country

Radiative, magnetic and numerical feedbacks on small-scale fragmentation

Radiative feedback and magnetic field are understood to have a strong impact on the protostellar collapse. We present high resolution numerical calculations of the collapse of a 1 solar mass dense core in solid body rotation, including both radiative transfer and magnetic field. Using typical parameters for low-mass cores, we study thoroughly the effect of radiative transfer and magnetic field on the first core formation and fragmentation. We show that including the two aforementioned physical processes does not correspond to the simple picture of adding them separately. The interplay between the two is extremely strong, via the magnetic braking and the radiation from the accretion shock.Comment: 4 pages, 2 figures ; to appear in "IAU Symposium 270: Computational Star formation", Eds. J. Alves, B. Elmegreen, J. Girart, V. Trimbl