10,006 research outputs found
Dirac nodal pockets in the antiferromagnetic parent phase of FeAs superconductors
We show that previously measured small Fermi surface pockets within the
antiferromagnetic phase of SrFe2As2 and BaFe2As2 are consistent with a Dirac
dispersion modulated by interlayer hopping, giving rise to a Dirac point in
k-space and a cusp in the magnetic field angle-dependent magnetic quantum
oscillation frequencies. These findings support the existence of a nodal
spin-density wave in these materials, which could play an important role in
protecting the metallic state against localization effects. The speed of the
Dirac fermions in SrFe2As2 and BaFe2As2 is found to be 14-20 times slower than
in graphene, suggesting that the pnictides provide a laboratory for exploring
the effects of strongly interacting Dirac fermions.Comment: 4 page
Prediction of unsteady aerodynamic loadings caused by leading edge and trailing edge control surface motions in subsonic compressible flow: Analysis and results
A theoretical analysis and computer program was developed for the prediction of unsteady lifting surface loadings caused by motions of leading edge and trailing edge control surfaces having sealed gaps. The final form of the downwash integral equation was formulated by isolating the singularities from the nonsingular terms and using a preferred solution process to remove and evaluate the downwash discontinuities in a systematic manner. Comparisons of theoretical and experimental pressure data are made for several control surface configurations. The comparisons indicate that reasonably accurate theoretical pressure distributions and generalized forces may be obtained for a wide variety of control surface configurations. Spanwise symmetry or antisymmetry of motion, and up to six control surfaces on each half span can be accommodated
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