12,280 research outputs found
Correlation between Spin Polarization and Magnetic Moment in Ferromagnetic Alloys
The correlation between the magnetic moment in ferromagnetic alloys and the
tunneling spin polarization in ferromagnet-insulator-superconductor tunneling
experiments has been a mystery. The measured spin polarization for Fe, Co, Ni,
and various Ni alloys is positive and roughly proportional to their magnetic
moments, which can not be explained by considering the net density of states.
Using a tight-binding coherent potential approximation (CPA) model, we show
that while the polarization of the net density of states is not correlated with
the magnetic moment, the polarization of the density of states of {\it s}
electrons is correlated with the magnetic moment in the same manner as observed
by the tunneling experiments.
We also discuss the spin polarization measurements by Andreev reflection
experiments, some of which obtained different results from the tunneling
experiments and our calculations.Comment: 8 RevTEX pages, 9 figures in ep
Computation of turbulent boundary layer flows with an algebraic stress turbulence model
An algebraic stress turbulence model is presented, characterized by the following: (1) the eddy viscosity expression is derived from the Reynolds stress turbulence model; (2) the turbulent kinetic energy dissipation rate equation is improved by including a production range time scale; and (3) the diffusion coefficients for turbulence equations are adjusted so that the kinetic energy profile extends further into the free stream region found in most experimental data. The turbulent flow equations were solved using a finite element method. Examples include: fully developed channel flow, fully developed pipe flow, flat plate boundary layer flow, plane jet exhausting into a moving stream, circular jet exhausting into a moving stream, and wall jet flow. Computational results compare favorably with experimental data for most of the examples considered. Significantly improved results were obtained for the plane jet flow, the circular jet flow, and the wall jet flow; whereas the remainder are comparable to those obtained by finite difference methods using the standard kappa-epsilon turbulence model. The latter seems to be promising with further improvement of the expression for the eddy viscosity coefficient
Semiconductor quantum dots in high magnetic fields: The composite-fermion view
We review and extend the composite fermion theory for semiconductor quantum
dots in high magnetic fields. The mean-field model of composite fermions is
unsatisfactory for the qualitative physics at high angular momenta. Extensive
numerical calculations demonstrate that the microscopic CF theory, which
incorporates interactions between composite fermions, provides an excellent
qualitative and quantitative account of the quantum dot ground state down to
the largest angular momenta studied, and allows systematic improvements by
inclusion of mixing between composite fermion Landau levels (called
levels).Comment: 13 pages, 8 figure
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