38,655 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
Waveguide mode imaging and dispersion analysis with terahertz near-field microscopy
Propagation of terahertz waves in hollow metallic waveguides depends on the waveguide mode. Near-field scanning probe terahertz microscopy is applied to identify the mode structure and composition in dielectric-lined hollow metallic waveguides. Spatial profiles, relative amplitudes, and group velocities of three main waveguide modes are experimentally measured and matched to the HE11, HE12, and TE11 modes. The combination of near-field microscopy with terahertz time-resolved spectroscopy opens the possibility of waveguide mode characterization in the terahertz band
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
A Chemical Survey of the Batang Belungkung River and the Gombak River
A chemical survey of water quality in the Batang Belungkung River and the Gombak River was conducted
to assess the degree of pollution due to the continuing discharge of rubber and domestic wastes.
Levels of dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD),
nutrients (phosphorus and nitrogen), solid and trace elements (sodium, potassium, calcium and magnesium)
were monitored sequentially downriver. The Batang Belungkung River was found to be severely polluted
with anaerobic conditions existing downriver. The upper region of the Gombak River was relatively unpolluted
while the lower region of the Gombak River was found to be severely polluted. An increase of
approximately fourteen-fold was found in the oxygen demand in the lower region of the Gombak River
over the ten year period from 1968/69 to 1978/79
Carrier and polarization dynamics in monolayer MoS2
In monolayer MoS2 optical transitions across the direct bandgap are governed
by chiral selection rules, allowing optical valley initialization. In time
resolved photoluminescence (PL) experiments we find that both the polarization
and emission dynamics do not change from 4K to 300K within our time resolution.
We measure a high polarization and show that under pulsed excitation the
emission polarization significantly decreases with increasing laser power. We
find a fast exciton emission decay time on the order of 4ps. The absence of a
clear PL polarization decay within our time resolution suggests that the
initially injected polarization dominates the steady state PL polarization. The
observed decrease of the initial polarization with increasing pump photon
energy hints at a possible ultrafast intervalley relaxation beyond the
experimental ps time resolution. By compensating the temperature induced change
in bandgap energy with the excitation laser energy an emission polarization of
40% is recovered at 300K, close to the maximum emission polarization for this
sample at 4K.Comment: 7 pages, 7 figures including supplementary materia
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