15,577 research outputs found
The Photonic Band theory and the negative refraction experiment of metallic helix metamaterials
We develop a theory to compute and interpret the photonic band structure of a
periodic array of metallic helices for the first time. Interesting features of
band structure include the ingenuous longitudinal and circularly polarized
eigenmodes, the wide polarization gap [Science 325, 1513 (2009)], and the
helical symmetry guarantees the existence of negative group velocity bands at
both sides of the polarization gap and band crossings pinned at the zone
boundary with fixed frequencies. A direct proof of negative refraction via a
chiral route [Science 306, 1353 (2004)] is achieved for the first time by
measuring Gooshanchen shift through a slab of three dimensional bona fide helix
metamaterial
Experimental realization of a broadband illusion optics device
We experimentally demonstrate the first metamaterial "illusion optics" device
- an "invisible gateway" by using a transmission-line medium. The device
contains an open channel that can block electromagnetic waves at a particular
frequency range. We also demonstrate that such a device can work in a broad
frequency range.Comment: 9 pages, 5 figure
Azimuthal distributions of radial momentum and velocity in relativistic heavy ion collisions
Azimuthal distributions of radial (transverse) momentum, mean radial
momentum, and mean radial velocity of final state particles are suggested for
relativistic heavy ion collisions. Using transport model AMPT with string
melting, these distributions for Au + Au collisions at 200 GeV are presented
and studied. It is demonstrated that the distribution of total radial momentum
is more sensitive to the anisotropic expansion, as the anisotropies of final
state particles and their associated transverse momentums are both counted in
the measure. The mean radial velocity distribution is compared with the radial
{\deg}ow velocity. The thermal motion contributes an isotropic constant to mean
radial velocity
Avalanche to streamer transition in particle simulations
The avalanche-to-streamer transition is studied and illustrated in a particle model. The results are similar to those of fluid models. However, when superparticles are introduced, numerical artifacts become visible. This underscores the need of models that are hybrid in space
Kinematics of the X-shaped Milky Way Bulge: Expectations from a Self-consistent N-body Model
We explore the kinematics (both the radial velocity and the proper motion) of
the vertical X-shaped feature in the Milky Way with an N-body bar/bulge model.
From the solar perspective, the distance distribution of particles is
double-peaked in fields passing through the X-shape. The separation and
amplitude ratio between the two peaks qualitatively match the observed trends
towards the Galactic bulge. We confirm clear signatures of cylindrical rotation
in the pattern of mean radial velocity across the bar/bulge region. We also
find possible imprints of coherent orbital motion inside the bar structure in
the radial velocity distribution along l=0 degree, where the near and far sides
of the bar/bulge show excesses of approaching and receding particles. The
coherent orbital motion is also reflected in the slight displacement of the
zero-velocity-line in the mean radial velocity, and the displacement of the
maximum/minimum in the mean longitudinal proper motion across the bulge region.
We find some degree of anisotropy in the stellar velocity within the X-shape,
but the underlying orbital family of the X-shape cannot be clearly
distinguished. Two potential applications of the X-shape in previous literature
are tested, i.e., bulge rotation and Galactic center measurements. We find that
the proper motion difference between the two sides of the X-shape can be used
to estimate the mean azimuthal streaming motion of the bulge, but not the
pattern speed of the bar. We also demonstrate that the Galactic center can be
located with the X-shape, but the accuracy depends on the fitting scheme, the
number of fields, and their latitudinal coverage.Comment: Minor changes to match the ApJ accepted version; 17 pages; emulateapj
format. The electronic tables of our model result are available upon reques
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