6,596 research outputs found
Abnormal enhancement of electric field inside a thin permittivity-near-zero object in free space
It is found that the electric field can be enhanced strongly inside a
permittivity-near-zero object in free space, when the transverse cross section
of the object is small and the length along the propagation direction of the
incident wave is large enough as compared with the wavelength. The physical
mechanism is explained in details. The incident electromagnetic energy can only
flow almost normally through the outer surface into or out of the
permittivity-near-zero object, which leads to large energy stream density and
then strong electric field inside the object. Meanwhile, the magnetic field
inside the permittivity-near-zero object may be smaller than that of the
incident wave, which is also helpful for enhancing the electric field. Two
permittivity-near-zero objects of simple shapes, namely, a thin cylindrical
shell and a long thin rectangular bar, are chosen for numerical illustration.
The enhancement of the electric field becomes stronger when the
permittivity-near-zero object becomes thinner. The physical mechanism of the
field enhancement is completely different from the plasmonic resonance
enhancement at a metal surface
Squeezing electromagnetic energy with a dielectric split ring inside a permeability-near-zero metamaterial
A novel electromagnetic energy squeezing mechanism is proposed based on the
special properties of permeability-near-zero metamaterials. Nearly no energy
stream can enter a conventional dielectric region positioned inside a
permeability-near-zero material. When a source is surrounded by a dielectric
split ring (encloser with a gap opened), the electromagnetic energy generated
by the source is forced to propagate through the gap. When the gap is narrow,
the energy stream density becomes very large and makes the magnetic field
enhanced drastically in the gap. The narrow gap can be long and bended. This
provides us a method to obtain strong magnetic field without using resonance
enhancement.Comment: 17pages, 4 figure
Spatio-temporal Keyframe Control of Traffic Simulation using Coarse-to-Fine Optimization
We present a novel traffic trajectory editing method which uses
spatio-temporal keyframes to control vehicles during the simulation to generate
desired traffic trajectories. By taking self-motivation, path following and
collision avoidance into account, the proposed force-based traffic simulation
framework updates vehicle's motions in both the Frenet coordinates and the
Cartesian coordinates. With the way-points from users, lane-level navigation
can be generated by reference path planning. With a given keyframe, the
coarse-to-fine optimization is proposed to efficiently generate the plausible
trajectory which can satisfy the spatio-temporal constraints. At first, a
directed state-time graph constructed along the reference path is used to
search for a coarse-grained trajectory by mapping the keyframe as the goal.
Then, using the information extracted from the coarse trajectory as
initialization, adjoint-based optimization is applied to generate a finer
trajectory with smooth motions based on our force-based simulation. We validate
our method with extensive experiments
On Spectral Graph Embedding: A Non-Backtracking Perspective and Graph Approximation
Graph embedding has been proven to be efficient and effective in facilitating
graph analysis. In this paper, we present a novel spectral framework called
NOn-Backtracking Embedding (NOBE), which offers a new perspective that
organizes graph data at a deep level by tracking the flow traversing on the
edges with backtracking prohibited. Further, by analyzing the non-backtracking
process, a technique called graph approximation is devised, which provides a
channel to transform the spectral decomposition on an edge-to-edge matrix to
that on a node-to-node matrix. Theoretical guarantees are provided by bounding
the difference between the corresponding eigenvalues of the original graph and
its graph approximation. Extensive experiments conducted on various real-world
networks demonstrate the efficacy of our methods on both macroscopic and
microscopic levels, including clustering and structural hole spanner detection.Comment: SDM 2018 (Full version including all proofs
4-[3-(BromoÂmethÂyl)benzÂyloxy]-3-methoxyÂbenzaldehyde
In the title compound, C16H15BrO3, the dihedral angle between the mean planes of the two benzene rings is 76.64 (2)°. In the crystal structure, there are weak π–π stacking interÂactions, with a centroid–centroid distance of 3.724 (3) Å, as well as an interÂmolecular C⋯Br distance [3.495 (2) Å] which is slightly less than the sum of the van der Waals radii for these atoms
- …