3,066 research outputs found
Homogenization of nonlocal wire metamaterial via a renormalization approach
It is well known that defining a local refractive index for a metamaterial
requires that the wavelength be large with respect to the scale of its
microscopic structure (generally the period). However, the converse does not
hold. There are simple structures, such as the infinite, perfectly conducting
wire medium, which remain non-local for arbitrarily large wavelength-to-period
ratios. In this work we extend these results to the more realistic and relevant
case of finite wire media with finite conductivity. In the quasi-static regime
the metamaterial is described by a non-local permittivity which is obtained
analytically using a two-scale renormalization approach. Its accuracy is tested
and confirmed numerically via full vector 3D finite element calculations.
Moreover, finite wire media exhibit large absorption with small reflection,
while their low fill factor allows considerable freedom to control other
characteristics of the metamaterial such as its mechanical, thermal or chemical
robustness.Comment: 8 pages on two columns, 7 figures, submitted to Phys. Rev.
Evaluation of noise immunity of high orbital satellite telecommunication systems with broadband noise-like sign
HIn with this regard article assesses the noise immunity of high-orbit satellite telecommunication systems with code division of addresses when using a number of broadband noise-like signals with linear frequency modulation as information carrier
Noncommutative Field Theories and (Super)String Field Theories
In this lecture notes we explain and discuss some ideas concerning
noncommutative geometry in general, as well as noncommutative field theories
and string field theories. We consider noncommutative quantum field theories
emphasizing an issue of their renormalizability and the UV/IR mixing. Sen's
conjectures on open string tachyon condensation and their application to the
D-brane physics have led to wide investigations of the covariant string field
theory proposed by Witten about 15 years ago. We review main ingredients of
cubic (super)string field theories using various formulations: functional,
operator, conformal and the half string formalisms. The main technical tools
that are used to study conjectured D-brane decay into closed string vacuum
through the tachyon condensation are presented. We describe also methods which
are used to study the cubic open string field theory around the tachyon vacuum:
construction of the sliver state, ``comma'' and matrix representations of
vertices.Comment: 160 pages, LaTeX, 29 EPS figures. Lectures given by I.Ya.Aref'eva at
the Swieca Summer School, Brazil, January 2001; Summer School in Modern
Mathematical Physics, Sokobanja, Yugoslavia, August 2001; Max Born Symposium,
Karpacz, Poland, September, 2001; Workshop "Noncommutative Geometry, Strings
and Renormalization", Leipzig, Germany, September 2001. Typos corrected,
references adde
Sub-wavelength imaging at optical frequencies using canalization regime
Imaging with sub-wavelength resolution using a lens formed by periodic
metal-dielectric layered structure is demonstrated. The lens operates in
canalization regime as a transmission device and it does not involve negative
refraction and amplification of evanescent modes. The thickness of the lens
have to be an integer number of half-wavelengths and can be made as large as
required for ceratin applications, in contrast to the other sub-wavelength
lenses formed by metallic slabs which have to be much smaller than the
wavelength. Resolution of at 600 nm wavelength is confirmed by
numerical simulation for a 300 nm thick structure formed by a periodic stack of
10 nm layers of glass with and 5 nm layers of metal-dielectric
composite with . Resolution of is predicted for a
structure with same thickness, period and operating frequency, but formed by
7.76 nm layers of silicon with and 7.24 nm layers of silver with
.Comment: 4 pages, 4 figures, submitted to PR
Pisgah Lava Cave Communication Test: Science Case Study for the Networked Constellations Initiative
As part of the science case study for the Networked Constellations initiative, a team of JPL scientists explore the possibility of a mission to study the lava caves on Mars. Natural caves on Mars and the Moon present a unique opportunity to learn about the planetary geology and to provide a shelter for human explorers. Due to power and communication challenges, a network of assets has significant advantages over a single asset sent inside a cave. However, communication between the assets and the data downlink present significant difficulties due to the presence of rough walls, boulders, and other obstacles with unknown dielectric constant inside a typical cave, disturbing the propagation of the radio waves. A detailed study is needed to establish the limitations of the current communication technologies and to develop requirements for the new communication technology applicable to the cave environment. On May 4 of 2017, Konstantin Belov, Doug Ellison, and Abby Fraeman visited a lava cave in Pisgah, CA. The purpose of the visit was to build a 3D map of the cave, which could be used to create a model of radio wave propagation, and to conduct a series of communication tests using off-the-shelf equipment to verify the in-cave communication challenges. This experiment should be considered as a simple 'proof of concept' and is the subject of this report
Global Spinors and Orientable Five-Branes
Fermion fields on an M-theory five-brane carry a representation of the double
cover of the structure group of the normal bundle. It is shown that, on an
arbitrary oriented Lorentzian six-manifold, there is always an Sp(2) twist that
allows such spinors to be defined globally. The vanishing of the arising
potential obstructions does not depend on spin structure in the bulk, nor does
the six-manifold need to be spin or spin-C. Lifting the tangent bundle to such
a generalised spin bundle requires picking a generalised spin structure in
terms of certain elements in the integral and modulo-two cohomology of the
five-brane world-volume in degrees four and five, respectively.Comment: 18 pages, LaTeX; v2: version to appear in JHE
Sub-wavelength imaging at infrared frequencies using an array of metallic nanorods
We demonstrate that an array of metallic nanorods enables sub-wavelength
(near-field) imaging at infrared frequencies. Using an homogenization approach,
it is theoretically proved that under certain conditions the incoming radiation
can be transmitted by the array of nanorods over a significant distance with
fairly low attenuation. The propagation mechanism does not involve a resonance
of material parameters and thus the resolution is not strongly affected by
material losses and has wide bandwidth. The sub-wavelength imaging with
resolution by silver rods at 30 THz is demonstrated numerically
using full-wave electromagnetic simulator.Comment: 12 pages, 16 figures, submitted to PR
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