33,106 research outputs found
Perfect Anomalous Reflection with a Binary Huygens' Metasurface
In this paper we propose a new metasurface that is able to reflect a known
incoming electromagnetic wave into an arbitrary direction, with perfect power
efficiency. This seemingly simple task, which we hereafter call perfect
anomalous reflection, is actually highly non-trivial due to the differing wave
impedances and complex interference between the incident and reflected waves.
Heretofore, proposed metasurfaces which achieve perfect anomalous reflection
require complicated, deeply subwavelength and/or multilayer element structures
which allow them to couple to and from leaky and/or evanescent waves. In
contrast, we demonstrate that using a Binary Huygens' Metasurface (BHM) --- a
passive and lossless metasurface with only two cells per period --- perfect
anomalous reflection can be achieved over a wide angular and frequency range.
Through simulations and experiments at 24 GHz, we show that a properly designed
BHM can anomalously reflect an incident electromagnetic wave from to , with perfect power efficiency to within
experimental precision
Relativistic Modification of the Gamow Factor
In processes involving Coulomb-type initial- and final-state interactions,
the Gamow factor has been traditionally used to take into account these
additional interactions. The Gamow factor needs to be modified when the
magnitude of the effective coupling constant increases or when the velocity
increases. For the production of a pair of particles under their mutual
Coulomb-type interaction, we obtain the modification of the Gamow factor in
terms of the overlap of the Feynman amplitude with the relativistic wave
function of the two particles. As a first example, we study the modification of
the Gamow factor for the production of two bosons. The modification is
substantial when the coupling constant is large.Comment: 13 pages, in LaTe
Elliptic Flow from a Transversally Thermalized Fireball
The agreement of elliptic flow data at RHIC at central rapidity with the
hydrodynamic model has led to the conclusion of very rapid thermalization. This
conclusion is based on the intuitive argument that hydrodynamics, which assumes
instantaneous local thermalization, produces the largest possible elliptic flow
values and that the data seem to saturate this limit. We here investigate the
question whether incompletely thermalized viscous systems may actually produce
more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast
primordial longitudinal expansion of the reaction zone, we investigate a toy
model which exhibits thermalization only in the transverse directions but
undergoes collisionless free-streaming expansion in the longitudinal direction.
For collisions at RHIC energies, elliptic flow results from the model are
compared with those from hydrodynamics. With the final particle yield and
\kt-distribution fixed, the transversally thermalized model is shown not to
be able to produce the measured amount of elliptic flow. This investigation
provides further support for very rapid local kinetic equilibration at RHIC. It
also yields interesting novel results for the elliptic flow of massless
particles such as direct photons.Comment: revtex4, 15 pages + 10 embedded EPS figure
A spatially shifted beam approach to subwavelength focusing
Although negative-refractive-index metamaterials have successfully achieved
subwavelength focusing, image resolution is limited by the presence of losses.
In this Letter, a metal transmission screen with subwavelength spaced slots is
proposed that focuses the near-field beyond the diffraction limit and
furthermore, is easily scaled from microwave frequencies to the optical regime.
An analytical model based on the superposition of shifted beam patterns is
developed that agrees very well with full-wave simulations and is corroborated
by experimental results at microwave frequencies.Comment: 5 pages, 7 figures. Content updated following reviewer comments to
match final published pape
Interference effects in f-deformed fields
We show how the introduction of an algeabric field deformation affects the
interference phenomena. We also give a physical interpretation of the developed
theory.Comment: 6 pages, Latex file, no figures, accepted by Physica Script
Angularly localized Skyrmions
Quantized Skyrmions with baryon numbers and 4 are considered and
angularly localized wavefunctions for them are found. By combining a few low
angular momentum states, one can construct a quantum state whose spatial
density is close to that of the classical Skyrmion, and has the same
symmetries. For the B=1 case we find the best localized wavefunction among
linear combinations of and angular momentum states. For B=2, we
find that the ground state has toroidal symmetry and a somewhat reduced
localization compared to the classical solution. For B=4, where the classical
Skyrmion has cubic symmetry, we construct cubically symmetric quantum states by
combining the ground state with the lowest rotationally excited
state. We use the rational map approximation to compare the classical and
quantum baryon densities in the B=2 and B=4 cases.Comment: 22 page
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