1,980 research outputs found
Behavior of different numerical schemes for population genetic drift problems
In this paper, we focus on numerical methods for the genetic drift problems,
which is governed by a degenerated convection-dominated parabolic equation. Due
to the degeneration and convection, Dirac singularities will always be
developed at boundary points as time evolves. In order to find a \emph{complete
solution} which should keep the conservation of total probability and
expectation, three different schemes based on finite volume methods are used to
solve the equation numerically: one is a upwind scheme, the other two are
different central schemes. We observed that all the methods are stable and can
keep the total probability, but have totally different long-time behaviors
concerning with the conservation of expectation. We prove that any extra
infinitesimal diffusion leads to a same artificial steady state. So upwind
scheme does not work due to its intrinsic numerical viscosity. We find one of
the central schemes introduces a numerical viscosity term too, which is beyond
the common understanding in the convection-diffusion community. Careful
analysis is presented to prove that the other central scheme does work. Our
study shows that the numerical methods should be carefully chosen and any
method with intrinsic numerical viscosity must be avoided.Comment: 17 pages, 8 figure
A Comparative Study on Spin-Orbit Torque Efficiencies from W/ferromagnetic and W/ferrimagnetic Heterostructures
It has been shown that W in its resistive form possesses the largest
spin-Hall ratio among all heavy transition metals, which makes it a good
candidate for generating efficient dampinglike spin-orbit torque (DL-SOT)
acting upon adjacent ferromagnetic or ferrimagnetic (FM) layer. Here we provide
a systematic study on the spin transport properties of W/FM magnetic
heterostructures with the FM layer being ferromagnetic
CoFeB or ferrimagnetic CoTb with
perpendicular magnetic anisotropy. The DL-SOT efficiency , which is
characterized by a current-induced hysteresis loop shift method, is found to be
correlated to the microstructure of W buffer layer in both
W/CoFeB and W/CoTb systems. Maximum values
of and are achieved when
the W layer is partially amorphous in the W/CoFeB and
W/CoTb heterostructures, respectively. Our results suggest that
the spin Hall effect from resistive phase of W can be utilized to effectively
control both ferromagnetic and ferrimagnetic layers through a DL-SOT mechanism
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