156 research outputs found
Zonal shear and super-rotation in a magnetized spherical Couette flow experiment
We present measurements performed in a spherical shell filled with liquid
sodium, where a 74 mm-radius inner sphere is rotated while a 210 mm-radius
outer sphere is at rest. The inner sphere holds a dipolar magnetic field and
acts as a magnetic propeller when rotated. In this experimental set-up called
DTS, direct measurements of the velocity are performed by ultrasonic Doppler
velocimetry. Differences in electric potential and the induced magnetic field
are also measured to characterize the magnetohydrodynamic flow. Rotation
frequencies of the inner sphere are varied between -30 Hz and +30 Hz, the
magnetic Reynolds number based on measured sodium velocities and on the shell
radius reaching to about 33. We have investigated the mean axisymmetric part of
the flow, which consists of differential rotation. Strong super-rotation of the
fluid with respect to the rotating inner sphere is directly measured. It is
found that the organization of the mean flow does not change much throughout
the entire range of parameters covered by our experiment. The direct
measurements of zonal velocity give a nice illustration of Ferraro's law of
isorotation in the vicinity of the inner sphere where magnetic forces dominate
inertial ones. The transition from a Ferraro regime in the interior to a
geostrophic regime, where inertial forces predominate, in the outer regions has
been well documented. It takes place where the local Elsasser number is about
1. A quantitative agreement with non-linear numerical simulations is obtained
when keeping the same Elsasser number. The experiments also reveal a region
that violates Ferraro's law just above the inner sphere.Comment: Phys Rev E, in pres
Age and skill bias of trade liberalisation? : heterogeneous employment effects of EU Eastern Enlargement
This study analyses the 2004 Eastern Enlargement to the European Union to
obtain evidence on the employment effects of an increase in trade liberalisation. The
Enlargement is thought to generate a trade-induced demand shock with no (or only
limited) supply effects. Besides the variation over time induced by the Enlargement,
identification of the effects is based on a Melitz (2003) type productivity term to
differentiate firms by the extent of exposure to the demand shock. The idea is that the
effects of the demand shock should be driven by differences in firm-level productivity
from the period before the new member countries actually entered the EU. German
linked employer-employee data allow to observe the relation of initial establishment
productivity with employment changes over a long panel from 1995 to 2009. The
estimates show that the Enlargement had a negative effect on establishment-level
employment growth, which is driven by increased worker separations and increased
job destruction. Besides the overall employment effect, the study focuses on effect
heterogeneity across age and skill groups of the workforce. These estimates point to a
skill bias in the effect of the Enlargement that disadvantages low- and medium-skilled
workers in terms of higher worker separation and job destruction. In addition, lowskilled
workers suffer fewer accessions by firms, where against medium-skilled workers
enjoy increased accessions and creation of new jobs. Besides this indication for a skill
bias, there are no clear indications that point to an age bias in the employment effect
of the Eastern Enlargement
Solubility of Rock in Steam Atmospheres of Planets
Extensive experimental studies show that all major rock-forming elements (e.g., Si, Mg, Fe, Ca, Al, Na, K) dissolve in steam to a greater or lesser extent. We use these results to compute chemical equilibrium abundances of rocky-element-bearing gases in steam atmospheres equilibrated with silicate magma oceans. Rocky elements partition into steam atmospheres as volatile hydroxide gases (e.g., Si(OH)4, Mg(OH)2, Fe(OH)2, Ni(OH)2, Al(OH)3, Ca(OH)2, NaOH, KOH) and via reaction with HF and HCl as volatile halide gases (e.g., NaCl, KCl, CaFOH, CaClOH, FAl(OH)2) in much larger amounts than expected from their vapor pressures over volatile-free solid or molten rock at high temperatures expected for steam atmospheres on the early Earth and hot rocky exoplanets. We quantitatively compute the extent of fractional vaporization by defining gas/magma distribution coefficients and show that Earth's subsolar Si/Mg ratio may be due to loss of a primordial steam atmosphere. We conclude that hot rocky exoplanets that are undergoing or have undergone escape of steam-bearing atmospheres may experience fractional vaporization and loss of Si, Mg, Fe, Ni, Al, Ca, Na, and K. This loss can modify their bulk composition, density, heat balance, and interior structure
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