44,235 research outputs found
Plasmonic Cloaking of Cylinders: Finite Length, Oblique Illumination and Cross-Polarization Coupling
Metamaterial cloaking has been proposed and studied in recent years following
several interesting approaches. One of them, the scattering-cancellation
technique, or plasmonic cloaking, exploits the plasmonic effects of suitably
designed thin homogeneous metamaterial covers to drastically suppress the
scattering of moderately sized objects within specific frequency ranges of
interest. Besides its inherent simplicity, this technique also holds the
promise of isotropic response and weak polarization dependence. Its theory has
been applied extensively to symmetrical geometries and canonical 3D shapes, but
its application to elongated objects has not been explored with the same level
of detail. We derive here closed-form theoretical formulas for infinite
cylinders under arbitrary wave incidence, and validate their performance with
full-wave numerical simulations, also considering the effects of finite lengths
and truncation effects in cylindrical objects. In particular, we find that a
single isotropic (idealized) cloaking layer may successfully suppress the
dominant scattering coefficients of moderately thin elongated objects, even for
finite lengths comparable with the incident wavelength, providing a weak
dependence on the incidence angle. These results may pave the way for
application of plasmonic cloaking in a variety of practical scenarios of
interest.Comment: 17 pages, 11 figures, 2 table
Efficient Prediction Designs for Random Fields
For estimation and predictions of random fields it is increasingly
acknowledged that the kriging variance may be a poor representative of true
uncertainty. Experimental designs based on more elaborate criteria that are
appropriate for empirical kriging are then often non-space-filling and very
costly to determine. In this paper, we investigate the possibility of using a
compound criterion inspired by an equivalence theorem type relation to build
designs quasi-optimal for the empirical kriging variance, when space-filling
designs become unsuitable. Two algorithms are proposed, one relying on
stochastic optimization to explicitly identify the Pareto front, while the
second uses the surrogate criteria as local heuristic to chose the points at
which the (costly) true Empirical Kriging variance is effectively computed. We
illustrate the performance of the algorithms presented on both a simple
simulated example and a real oceanographic dataset
Clifford group dipoles and the enactment of Weyl/Coxeter group W(E8) by entangling gates
Peres/Mermin arguments about no-hidden variables in quantum mechanics are
used for displaying a pair (R, S) of entangling Clifford quantum gates, acting
on two qubits. From them, a natural unitary representation of Coxeter/Weyl
groups W(D5) and W(F4) emerges, which is also reflected into the splitting of
the n-qubit Clifford group Cn into dipoles Cn . The union of the
three-qubit real Clifford group C+ 3 and the Toffoli gate ensures a orthogonal
representation of the Weyl/Coxeter group W(E8), and of its relatives. Other
concepts involved are complex reflection groups, BN pairs, unitary group
designs and entangled states of the GHZ family.Comment: version revised according the recommendations of a refere
A "poor man's" approach to topology optimization of natural convection problems
Topology optimization of natural convection problems is computationally
expensive, due to the large number of degrees of freedom (DOFs) in the model
and its two-way coupled nature. Herein, a method is presented to reduce the
computational effort by use of a reduced-order model governed by simplified
physics. The proposed method models the fluid flow using a potential flow
model, which introduces an additional fluid property. This material property
currently requires tuning of the model by comparison to numerical Navier-Stokes
based solutions. Topology optimization based on the reduced-order model is
shown to provide qualitatively similar designs, as those obtained using a full
Navier-Stokes based model. The number of DOFs is reduced by 50% in two
dimensions and the computational complexity is evaluated to be approximately
12.5% of the full model. We further compare to optimized designs obtained
utilizing Newton's convection law.Comment: Preprint version. Please refer to final version in Structural
Multidisciplinary Optimization https://doi.org/10.1007/s00158-019-02215-
Intersection numbers for subspace designs
Intersection numbers for subspace designs are introduced and -analogs of
the Mendelsohn and K\"ohler equations are given. As an application, we are able
to determine the intersection structure of a putative -analog of the Fano
plane for any prime power . It is shown that its existence implies the
existence of a - subspace design. Furthermore, several
simplified or alternative proofs concerning intersection numbers of ordinary
block designs are discussed
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