20,862 research outputs found
Angular momentum transport and element mixing in the stellar interior I. Application to the rotating Sun
The purpose of this work was to obtain diffusion coefficient for the magnetic
angular momentum transport and material transport in a rotating solar model. We
assumed that the transport of both angular momentum and chemical elements
caused by magnetic fields could be treated as a diffusion process. The
diffusion coefficient depends on the stellar radius, angular velocity, and the
configuration of magnetic fields. By using of this coefficient, it is found
that our model becomes more consistent with the helioseismic results of total
angular momentum, angular momentum density, and the rotation rate in a
radiative region than the one without magnetic fields. Not only can the
magnetic fields redistribute angular momentum efficiently, but they can also
strengthen the coupling between the radiative and convective zones. As a
result, the sharp gradient of the rotation rate is reduced at the bottom of the
convective zone. The thickness of the layer of sharp radial change in the
rotation rate is about 0.036 in our model. Furthermore, the
difference of the sound-speed square between the seismic Sun and the model is
improved by mixing the material that is associated with angular momentum
transport.Comment: 8 pages, 2 figure
High efficiency n-type silicon solar cells featuring passivated contact to laser doped regions
Minimizing carrier recombination at cell contacts becomes increasingly important for reaching high efficiency. In this work, the passivated contact concept is implemented into n-type silicon solar cells with laser-processed local back surface fields. The passivation and contact characteristics of the SiO2/amorphous silicon (a-Si:H) stack on localized laser doped n+ regions are investigated. We find that the SiO2/a-Si:H stack provides not only good passivation to laser doped n+ regions but also allows a low contact resistivity after thermal annealing. With the implementation of the SiO2/a-Si:H passivated contact, an absolute efficiency gain of up to 1.5% is achieved for n-type solar cells
Solar Models with Revised Abundances and Opacities
Using reconstructed opacities, we construct solar models with low
heavy-element abundance. Rotational mixing and enhanced diffusion of helium and
heavy elements are used to reconcile the recently observed abundances with
helioseismology. The sound speed and density of models where the relative and
absolute diffusion coefficients for helium and heavy elements have been
increased agree with seismically inferred values at better than the 0.005 and
0.02 fractional level respectively. However, the surface helium abundance of
the enhanced diffusion model is too low. The low helium problem in the enhanced
diffusion model can be solved to a great extent by rotational mixing. The
surface helium and the convection zone depth of rotating model M04R3, which has
a surface Z of 0.0154, agree with the seismic results at the levels of 1
and 3 respectively. M04R3 is almost as good as the standard
model M98. Some discrepancies between the models constructed in accord with the
new element abundances and seismic constraints can be solved individually, but
it seems difficult to resolve them as a whole scenario.Comment: 10 pages, 1 figur
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