5,000 research outputs found
Transmission-Line Analysis of Epsilon-Near-Zero (ENZ)-Filled Narrow Channels
Following our recent interest in metamaterial-based devices supporting
resonant tunneling, energy squeezing and supercoupling through narrow waveguide
channels and bends, here we analyze the fundamental physical mechanisms behind
this phenomenon using a transmission-line model. These theoretical findings
extend our theory, allowing us to take fully into account frequency dispersion
and losses and revealing the substantial differences between this unique
tunneling phenomenon and higher-frequency Fabry-Perot resonances. Moreover,
they represent the foundations for other possibilities to realize tunneling
through arbitrary waveguide bends, both in E and H planes of polarization,
waveguide connections and sharp abruptions and to obtain analogous effects with
geometries arguably simpler to realize.Comment: 35 pages, 9 figure
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A Dense Reference Network for Mass-Market Centimeter-Accurate Positioning
The quality of atmospheric corrections provided
by a dense reference network for centimeter-accurate carrierphase
differential GNSS (CDGNSS) positioning is investigated.
A dense reference network (less than 20 km inter-station distance)
offers significant benefits for mass-market users, enabling lowcost
(including single-frequency) CDGNSS positioning with rapid
integer ambiguity resolution. Precise positioning on a massmarket
platform would significantly influence the world economy,
ushering in a host of consumer-focused applications such as
globally-registered augmented and virtual reality and improved
all-weather safety and efficiency for intelligent transportation
systems, applications which have so far been hampered by the
several-meter-level errors in standard GNSS positioning. This
contribution examines CDGNSS integer ambiguity resolution
performance in terms of network correction uncertainty, and
network correction uncertainty, in turn, in terms of network
density. It considers the total error in network corrections: a
sum of ionospheric, tropospheric, and reference station multipath
components. The paper’s primary goal is to identify the network
density beyond which mass-market users would see no further
significant improvement in ambiguity resolution performance. It
finishes by describing development and deployment of a low-cost
dense reference network in Austin, Texas.Aerospace Engineering and Engineering Mechanic
Electromagnetic surface states in structured perfect-conductor surfaces
Surface-bound modes in metamaterials forged by drilling periodic hole arrays
in perfect-conductor surfaces are investigated by means of both analytical
techniques and rigorous numerical solution of Maxwell's equations. It is shown
that these metamaterials cannot be described in general by local,
frequency-dependent permittivities and permeabilities for small periods
compared to the wavelength, except in certain limiting cases that are discussed
in detail. New related metamaterials are shown to exhibit exciting optical
properties that are elucidated in the light of our simple analytical approach.Comment: 5 figure
Center of mass rotation and vortices in an attractive Bose gas
The rotational properties of an attractively interacting Bose gas are studied
using analytical and numerical methods. We study perturbatively the ground
state phase space for weak interactions, and find that in an anharmonic trap
the rotational ground states are vortex or center of mass rotational states;
the crossover line separating these two phases is calculated. We further show
that the Gross-Pitaevskii equation is a valid description of such a gas in the
rotating frame and calculate numerically the phase space structure using this
equation. It is found that the transition between vortex and center of mass
rotation is gradual; furthermore the perturbative approach is valid only in an
exceedingly small portion of phase space. We also present an intuitive picture
of the physics involved in terms of correlated successive measurements for the
center of mass state.Comment: version2, 17 pages, 5 figures (3 eps and 2 jpg
POD-Galerkin advection model for convective flow Application to a flapping rectangular supersonic jet
International audienceThis article describes a model obtained by applying Proper Orthogonal Decomposition to the ad-vection equation. The resulting set of equations links the POD modes, their temporal and spatial derivatives and the flow convection velocity. It provides a technique to calculate the convection velocity of coherent structures. It follows, from the model, that a priori knowledge of the convection velocity suffices to construct a dynamical model of the flow. This is demonstrated using experimental data
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