6,876 research outputs found
Experimental verification of the "rainbow" trapping effect in plasmonic graded gratings
We report the first experimental observation of trapped rainbow1 in graded
metallic gratings2-4, designed to validate theoretical predictions for this new
class of plasmonic structures. One-dimensional tapered gratings were fabricated
and their surface dispersion properties tailored by varying the grating period
and depth, whose dimensions were confirmed by atomic force microscopy. Reduced
group velocities and the plasmonic bandgap were observed. Direct measurements
on graded grating structures show that light of different wavelengths in the
500-700nm region is "trapped" at different positions along the grating,
consistent with computer simulations, thus verifying the "rainbow" trapping
effect. The trapped rainbow effect offers exciting pathways for optical
information storage and optical delays in photonic circuits at ambient
temperature
Frequency variations of gravity waves interacting with a time-varying tide
Using a nonlinear, 2-D time-dependent numerical model, we simulate the
propagation of gravity waves (GWs) in a time-varying tide. Our simulations
show that when a GW packet propagates in a time-varying tidal-wind
environment, not only its intrinsic frequency but also its ground-based
frequency would change significantly. The tidal horizontal-wind acceleration
dominates the GW frequency variation. Positive (negative) accelerations
induce frequency increases (decreases) with time. More interestingly,
tidal-wind acceleration near the critical layers always causes the GW
frequency to increase, which may partially explain the observations that
high-frequency GW components are more dominant in the middle and upper
atmosphere than in the lower atmosphere. The combination of the increased
ground-based frequency of propagating GWs in a time-varying tidal-wind field
and the transient nature of the critical layer induced by a time-varying
tidal zonal wind creates favorable conditions for GWs to penetrate their
originally expected critical layers. Consequently, GWs have an impact on the
background atmosphere at much higher altitudes than expected, which indicates
that the dynamical effects of tidal–GW interactions are more complicated
than usually taken into account by GW parameterizations in global models
Possible Way to Synthesize Superheavy Element Z=117
Within the framework of the dinuclear system model, the production of
superheavy element Z=117 in possible projectile-target combinations is analyzed
systematically. The calculated results show that the production cross sections
are strongly dependent on the reaction systems. Optimal combinations,
corresponding excitation energies and evaporation channels are proposed in this
letter, such as the isotopes ^{248,249}Bk in ^{48}Ca induced reactions in 3n
evaporation channels and the reactions ^{45}Sc+^{246,248}Cm in 3n and 4n
channels, and the system ^{51}V+^{244}Pu in 3n channel.Comment: 10 pages, 4 figures, 1 tabl
Lattice Boltzmann study on Kelvin-Helmholtz instability: the roles of velocity and density gradients
A two-dimensional lattice Boltzmann model with 19 discrete velocities for
compressible Euler equations is proposed (D2V19-LBM). The fifth-order Weighted
Essentially Non-Oscillatory (5th-WENO) finite difference scheme is employed to
calculate the convection term of the lattice Boltzmann equation. The validity
of the model is verified by comparing simulation results of the Sod shock tube
with its corresponding analytical solutions. The velocity and density gradient
effects on the Kelvin-Helmholtz instability (KHI) are investigated using the
proposed model. Sharp density contours are obtained in our simulations. It is
found that, the linear growth rate for the KHI decreases with
increasing the width of velocity transition layer but increases with
increasing the width of density transition layer . After the
initial transient period and before the vortex has been well formed, the linear
growth rates, and , vary with and
approximately in the following way, and
, where , ,
and are fitting parameters and is the effective
interaction width of density transition layer. When
the linear growth rate does not vary significantly any more.
One can use the hybrid effects of velocity and density transition layers to
stabilize the KHI. Our numerical simulation results are in general agreement
with the analytical results [L. F. Wang, \emph{et al.}, Phys. Plasma
\textbf{17}, 042103 (2010)].Comment: Accepted for publication in PR
Lattice distortion and uniaxial magnetic anisotropy in single domain epitaxial (110) films of SrRuO3
The effects of epitaxial strain on the orthorhombic-to-triclinic lattice distortion and uniaxial magnetic anisotropy in single-domain SrRuO3 (110) films epitaxially grown on (001) SrTiO3 substrates were examined. The magnetic orientation of the film was found to be along or near the [010] direction, rotating towards the [110] perpendicular direction with decreasing temperature. The influence of the crystalline anisotropy in SrRuO3 on the uniaxial magnetic anisotropy was also examined
Instability of the Fermi-liquid fixed point in an extended Kondo model
We study an extended SU(N) single-impurity Kondo model in which the impurity
spin is described by a combination of Abrikosov fermions and Schwinger bosons.
Our aim is to describe both the quasiparticle-like excitations and the locally
critical modes observed in various physical situations, including non-Fermi
liquid (NFL) behavior in heavy fermions in the vicinity of a quantum critical
point and anomalous transport properties in quantum wires. In contrast with
models with either pure bosonic or pure fermionic impurities, the strong
coupling fixed point is unstable against the conduction electron kinetic term
under certain conditions. The stability region of the strong coupling fixed
point coincides with the region where the partially screened, effective
impurity repels the electrons on adjacent sites. In the instability region, the
impurity tends to attract electrons to the neighboring sites, giving
rise to a double-stage Kondo effect with additional screening of the impurity.Comment: 10 pages, 2 figures, Proceedings of the NATO Workshop on "Concepts in
Electron Correlations", Hvar,October 200
Mobile communication base station antenna measurement using unmanned aerial vehicle
Traditional base station antenna measurement methods conducted with professional worker climbing towers tend to raise safety and inefficiency concerns in practical application. Designed to address the above problems, this paper proposes an intelligent and fully automatic antenna measurement unmanned aerial vehicle (UAV) system for mobile communication base station. Firstly, an antenna database, containing 19,715 images, named UAV-Antenna is constructed by image capturing with the help of UAVs flying around various base stations. Secondly, Mask R-CNN is adopted to train an optimal instance segmentation model on UAV-Antenna. Then, pixel coordinates and threshold are utilized for measuring antenna quantity and separate all antenna data for further measuring. Finally, a least squares method is employed for measuring antenna parameters. Experimental results show that the proposed method can not only satisfy the industry application standards, but also guarantee safety of labors and efficiency of performance
Spin wave theory for antiferromagnetic XXZ spin model on a triangle lattice in the presence of an external magnetic field
Spin wave theory is applied to a quantum antiferromagnetic XXZ model on a
triangle lattice in the presence of an in-plane magnetic field. The effect of
the field is found to enhance the quantum fluctuation and to reduce the
sublattice magnetization at the intermediate field strength in the anisotropic
case. The possible implication to the field driven quantum phase transition
from a spin solid to a spin liquid is discussed.Comment: 5 pages,4 figure
Mesoscale magnetism at the grain boundaries in colossal magnetoresistive films
We report the discovery of mesoscale regions with distinctive magnetic
properties in epitaxial LaSrMnO films which exhibit
tunneling-like magnetoresistance across grain boundaries. By using
temperature-dependent magnetic force microscopy we observe that the mesoscale
regions are formed near the grain boundaries and have a different Curie
temperature (up to 20 K {\it higher}) than the grain interiors. Our images
provide direct evidence for previous speculations that the grain boundaries in
thin films are not magnetically and electronically sharp interfaces. The size
of the mesoscale regions varies with temperature and nature of the underlying
defect.Comment: 4 pages of text, 4 figure
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