547 research outputs found
Spatial dispersion and energy in strong chiral medium
Since the discovery of backward-wave materials, people have tried to realize
strong chiral medium, which is traditionally thought impossible mainly for the
reason of energy and spatial dispersion. We compare the two most popular
descriptions of chiral medium. After analyzing several possible reasons for the
traditional restriction, we show that strong chirality parameter leads to
positive energy without any frequency-band limitation in the weak spatial
dispersion. Moreover, strong chirality does not result in a strong spatial
dispersion, which occurs only around the traditional limit point. For strong
spatial dispersion where higher-order terms of spatial dispersion need to be
considered, the energy conversation is also valid. Finally, we show that strong
chirality need to be realized from the conjugated type of spatial dispersion.Comment: 6 pages, 2 figure
Generalized Cut-Set Bounds for Broadcast Networks
A broadcast network is a classical network with all source messages
collocated at a single source node. For broadcast networks, the standard
cut-set bounds, which are known to be loose in general, are closely related to
union as a specific set operation to combine the basic cuts of the network.
This paper provides a new set of network coding bounds for general broadcast
networks. These bounds combine the basic cuts of the network via a variety of
set operations (not just the union) and are established via only the
submodularity of Shannon entropy. The tightness of these bounds are
demonstrated via applications to combination networks.Comment: 30 pages, 4 figures, submitted to the IEEE Transaction on Information
Theor
Facilitating inter-municipal collaboration through mandated collaborative platform:Evidence from regional environmental protection in China
Negative reflections of electromagnetic waves in chiral media
We investigate the reflection properties of electromagnetic/optical waves in
isotropic chiral media. When the chiral parameter is strong enough, we show
that an unusual \emph{negative reflection} occurs at the interface of the
chiral medium and a perfectly conducting plane, where the incident wave and one
of reflected eigenwaves lie in the same side of the boundary normal. Using such
a property, we further demonstrate that such a conducting plane can be used for
focusing in the strong chiral medium. The related equations under paraxial
optics approximation are deduced. In a special case of chiral medium, the
chiral nihility, one of the bi-reflections disappears and only single reflected
eigenwave exists, which goes exactly opposite to the incident wave. Hence the
incident and reflected electric fields will cancel each other to yield a zero
total electric field. In another word, any electromagnetic waves entering the
chiral nihility with perfectly conducting plane will disappear.Comment: 5 pages, 5 figure
Fast and accurate simulations of transmission-line metamaterials using transmission-matrix method
Recently, two-dimensional (2D) periodically L and C loaded transmission-line
(TL) networks have been applied to represent metamaterials. The commercial
Agilent's Advanced Design System (ADS) is a commonly-used tool to simulate the
TL metamaterials. However, it takes a lot of time to set up the TL network and
perform numerical simulations using ADS, making the metamaterial analysis
inefficient, especially for large-scale TL networks. In this paper, we propose
transmission-matrix method (TMM) to simulate and analyze the TL-network
metamaterials efficiently. Compared to the ADS commercial software, TMM
provides nearly the same simulation results for the same networks. However, the
model-process and simulation time has been greatly reduced. The proposed TMM
can serve as an efficient tool to study the TL-network metamaterials.Comment: 15 pages, 13 figure
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