46,119 research outputs found
Valley filter in strain engineered graphene
We propose a simple, yet highly efficient and robust device for producing
valley polarized current in graphene. The device comprises of two distinct
components; a region of uniform uniaxial strain, adjacent to an out-of-plane
magnetic barrier configuration formed by patterned ferromagnetic gates. We show
that when the amount of strain, magnetic field strength, and Fermi level are
properly tuned, the output current can be made to consist of only a single
valley contribution. Perfect valley filtering is achievable within
experimentally accessible parameters.Comment: 4 pages, 3 figures; minor corrections, updated Figs. 2 and 3, added
reference
Non-equilibrium spatial distribution of Rashba spin torque in ferromagnetic metal layer
We study the spatial distribution of spin torque induced by a strong Rashba
spin-orbit coupling (RSOC) in a ferromagnetic (FM) metal layer, using the
Keldysh non-equilibrium Green's function method. In the presence of the s-d
interaction between the non-equilibrium conduction electrons and the local
magnetic moments, the RSOC effect induces a torque on the moments, which we
term as the Rashba spin torque.
A correlation between the Rashba spin torque and the spatial spin current is
presented in this work, clearly mapping the spatial distribution of Rashba Spin
torque in a nano-sized ferromagnetic device. When local magnetism is turned on,
the out-of-plane (Sz) Spin Hall effect (SHE) is disrupted, but rather
unexpectedly an in-plane (Sy) SHE is detected. We also study the effect of
Rashba strength (\alpha_R) and splitting exchange (\Delta) on the
non-equilibrium Rashba spin torque averaged over the device. Rashba spin torque
allows an efficient transfer of spin momentum such that a typical switching
field of 20 mT can be attained with a low current density of less than 10^6
A/cm^2
An integrated wind risk warning model for urban rail transport in Shanghai, China
The integrated wind risk warning model for rail transport presented has four elements:
Background wind data, a wind field model, a vulnerability model, and a risk model. Background
wind data uses observations in this study. Using the wind field model with effective surface
roughness lengths, the background wind data are interpolated to a 30-m resolution grid. In the
vulnerability model, the aerodynamic characteristics of railway vehicles are analyzed with CFD
(Computational Fluid Dynamics) modelling. In the risk model, the maximum value of three
aerodynamic forces is used as the criteria to evaluate rail safety and to quantify the risk level under
extremely windy weather. The full model is tested for the Shanghai Metro Line 16 using wind
conditions during Typhoon Chan-hom. The proposed approach enables quick quantification of real-
time safety risk levels during typhoon landfall, providing sophisticated warning information for
rail vehicle operation safety
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